Address data races seen with certain passive stream's parameters

18:00:14 WARNING: ThreadSanitizer: data race (pid=182831)

18:00:14   Write of size 4 at 0x7d5000018120 by thread T17 (mutexes: write M22779):

18:00:14     #0 PassiveStream::processMarker(SnapshotMarker*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/dcp-stream.cc:1439 (ep.so+0x00000029e32a)

18:00:14     #1 PassiveStream::processBufferedMessages(unsigned int&) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/dcp-stream.cc:1293 (ep.so+0x00000029d248)

18:00:14     #2 DcpConsumer::processBufferedItems() /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/dcp-consumer.cc:599 (ep.so+0x0000002634f4)

18:00:14     #3 Processer::run() /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/dcp-consumer.cc:48 (ep.so+0x0000002630ef)

18:00:14     #4 ExecutorThread::run() /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/executorthread.cc:109 (ep.so+0x0000001e3fe1)

18:00:14     #5 launch_executor_thread(void*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/executorthread.cc:34 (ep.so+0x0000001e360a)

18:00:14     #6 platform_thread_wrap /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/platform/src/cb_pthreads.c (libplatform.so.0.1.0+0x00000000377c)

18:00:14 

18:00:14   Previous read of size 4 at 0x7d5000018120 by main thread (mutexes: write M1052854040829931240, write M969):

18:00:14     #0 PassiveStream::addStats(void (*)(char const*, unsigned short, char const*, unsigned int, void const*), void const*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/dcp-stream.cc:1530 (ep.so+0x00000029fb1b)

18:00:14     #1 DcpConsumer::addStats(void (*)(char const*, unsigned short, char const*, unsigned int, void const*), void const*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/dcp-consumer.cc:555 (ep.so+0x00000026d5f7)

18:00:14     #2 ConnStatBuilder::operator()(SingleThreadedRCPtr<ConnHandler>&) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/ep_engine.cc:3701 (ep.so+0x000000183c44)

18:00:14     #3 ConnStatBuilder std::for_each<std::_List_iterator<SingleThreadedRCPtr<ConnHandler> >, ConnStatBuilder>(std::_List_iterator<SingleThreadedRCPtr<ConnHandler> >, std::_List_iterator<SingleThreadedRCPtr<ConnHandler> >, ConnStatBuilder) /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../../include/c++/4.9/bits/stl_algo.h:3755 (ep.so+0x0000001838a5)

18:00:14     #4 void ConnMap::each_UNLOCKED<ConnStatBuilder>(ConnStatBuilder) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/connmap.h:148 (ep.so+0x000000183808)

18:00:14     #5 void ConnMap::each<ConnStatBuilder>(ConnStatBuilder) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/connmap.h:140 (ep.so+0x00000017732e)

18:00:14     #6 EventuallyPersistentEngine::doDcpStats(void const*, void (*)(char const*, unsigned short, char const*, unsigned int, void const*)) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/ep_engine.cc:3954 (ep.so+0x00000014c5ed)

18:00:14     #7 EventuallyPersistentEngine::getStats(void const*, char const*, int, void (*)(char const*, unsigned short, char const*, unsigned int, void const*)) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/ep_engine.cc:4367 (ep.so+0x000000150f81)

18:00:14     #8 EvpGetStats(engine_interface*, void const*, char const*, int, void (*)(char const*, unsigned short, char const*, unsigned int, void const*)) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/src/ep_engine.cc:214 (ep.so+0x000000136f62)

18:00:14     #9 mock_get_stats /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/memcached/programs/engine_testapp/engine_testapp.c (engine_testapp+0x0000004c8403)

18:00:14     #10 get_int_stat(engine_interface*, engine_interface_v1*, char const*, char const*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/tests/ep_test_apis.cc:771 (ep_testsuite.so+0x0000000e1e5a)

18:00:14     #11 wait_for_stat_to_be(engine_interface*, engine_interface_v1*, char const*, int, char const*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/tests/ep_test_apis.cc:860 (ep_testsuite.so+0x0000000e899b)

18:00:14     #12 test_dcp_invalid_snapshot_marker(engine_interface*, engine_interface_v1*) /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/ep-engine/tests/ep_testsuite.cc:8680 (ep_testsuite.so+0x0000000a8445)

18:00:14     #13 execute_test /home/couchbase/jenkins/workspace/ep-engine-threadsanitizer-3.0.x/memcached/programs/engine_testapp/engine_testapp.c (engine_testapp+0x0000004c4e9f)

18:00:14     #14 main crtstuff.c (engine_testapp+0x0000004c2e01)