del_with_meta from 4.5 XDCR parsed incorrectly

Steps to reproduce

1. Created a single node cluster on Couchbase Server 4.5.1 with the default bucket
2. Created a single node cluster on Couchbase Server 4.6 with the default bucket
3. Create a XDCR replication from 4.5.1 to 4.6
4. Created a document called "test" in the UI on 4.5.1
5. Delete the document "test" in the UI on 4.5.1
6. xdcr logs now loop with the following messages:

   XmemNozzle 2017-03-02T03:13:12.798Z [INFO] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 - 1 unresponded items are resent

   XmemNozzle 2017-03-02T03:13:12.798Z [ERROR] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 received error response from setMeta client. Repairing connection. response status=EINVAL, opcode=0xa8, seqno=2, req.Key=test, req.Cas=0, req.Extras=[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 20 167 241 230 129 242 0 0 0 5]

   XmemNozzle 2017-03-02T03:13:12.798Z [ERROR] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 connection client_setMeta is broken due to error response from memcached, try to repair...

   ConnPoolMgr 2017-03-02T03:13:12.798Z [INFO] Successfully retrieved connection pool with name 68f00fa68c1400dc79369123d574dc0e/default/default/Couch_Xmem_10.111.160.101:11210/default

   XmemNozzle 2017-03-02T03:13:12.801Z [INFO] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 - The connection for client_setMeta has been repaired

   XmemNozzle 2017-03-02T03:13:12.801Z [INFO] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 - 1 unresponded items are resent

   XmemNozzle 2017-03-02T03:13:12.801Z [ERROR] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 received error response from setMeta client. Repairing connection. response status=EINVAL, opcode=0xa8, seqno=2, req.Key=test, req.Cas=0, req.Extras=[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 20 167 241 230 129 242 0 0 0 5]

   XmemNozzle 2017-03-02T03:13:12.801Z [ERROR] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 connection client_setMeta is broken due to error response from memcached, try to repair...

   ConnPoolMgr 2017-03-02T03:13:12.801Z [INFO] Successfully retrieved connection pool with name 68f00fa68c1400dc79369123d574dc0e/default/default/Couch_Xmem_10.111.160.101:11210/default

   XmemNozzle 2017-03-02T03:13:12.803Z [INFO] xmem_68f00fa68c1400dc79369123d574dc0e/default/default_10.111.160.101:11210_0 - The connection for client_setMeta has been repaired

   XmemNozzle 2017-03-02T03:13:12.804Z [INFO] xmem_68f00

Problem
XDCR stops syncing when it tries to send a tombstone (a delete) and will keeps looping with the error EINVAL