tap_count is reported incorrectly in the stats

tap_count is report as 0 even though there is a tap client is connected.

1. echo stats tap | nc localhost 11211                       
   STAT eq_tapq:xx.xx.xx.xx:11211:qlen 0
   STAT eq_tapq:xx.xx.xx.xx:11211:qlen_high_pri 0
   STAT eq_tapq:xx.xx.xx.xx:11211:qlen_low_pri 0
   STAT eq_tapq:xx.xx.xx.xx:11211:vb_filters 1
   STAT eq_tapq:xx.xx.xx.xx:11211:rec_fetched 6258771
   STAT eq_tapq:xx.xx.xx.xx:11211:idle true
   STAT eq_tapq:xx.xx.xx.xx:11211:empty true
   STAT eq_tapq:xx.xx.xx.xx:11211:complete false
   STAT eq_tapq:xx.xx.xx.xx:11211:has_item false
   STAT eq_tapq:xx.xx.xx.xx:11211:has_queued_item false
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_wait_for_results false
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_queue_size 0
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_queued 0
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_result_size 0
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_results 0
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_jobs_issued 0
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_jobs_completed 0
   STAT eq_tapq:xx.xx.xx.xx:11211:bg_backlog_size 0
   STAT eq_tapq:xx.xx.xx.xx:11211:flags 20
   STAT eq_tapq:xx.xx.xx.xx:11211:connected true
   STAT eq_tapq:xx.xx.xx.xx:11211:pending_disconnect false
   STAT eq_tapq:xx.xx.xx.xx:11211:paused true
   STAT eq_tapq:xx.xx.xx.xx:11211:pending_backfill false
   STAT eq_tapq:xx.xx.xx.xx:11211:reconnects 3
   STAT eq_tapq:xx.xx.xx.xx:11211:disconnects 3
   STAT eq_tapq:xx.xx.xx.xx:11211:ack_seqno 7294
   STAT eq_tapq:xx.xx.xx.xx:11211:recv_ack_seqno 7293
   STAT eq_tapq:xx.xx.xx.xx:11211:ack_log_size 0
   STAT eq_tapq:xx.xx.xx.xx:11211:ack_window_full false
   STAT ep_tap_total_queue 0
   STAT ep_tap_total_fetched 6253106
   STAT ep_tap_bg_max_pending 500
   STAT ep_tap_bg_fetched 0
   STAT ep_tap_fg_fetched 6253096
   STAT ep_tap_deletes 4
   STAT ep_tap_keepalive 600
   STAT ep_tap_noop_interval 200
   STAT ep_tap_count 0
   STAT ep_replication_state disabled
   STAT ep_tap_ack_window_size 10
   STAT ep_tap_ack_high_chunk_threshold 1000
   STAT ep_tap_ack_medium_chunk_threshold 100
   STAT ep_tap_ack_low_chunk_threshold 10
   STAT ep_tap_ack_grace_period 300
   END

1. echo stats | nc localhost 11211 | grep version
   STAT version 1.4.4_312_gdb51765
   STAT ep_version 1.6.3

1. /opt/membase/bin/ep_engine/management/stats localhost:11211 tap
    ep_replication_state:                           disabled
    ep_tap_ack_grace_period:                        300
    ep_tap_ack_high_chunk_threshold:                1000
    ep_tap_ack_low_chunk_threshold:                 10
    ep_tap_ack_medium_chunk_threshold:              100
    ep_tap_ack_window_size:                         10
    ep_tap_bg_fetched:                              0
    ep_tap_bg_max_pending:                          500
    ep_tap_count:                                   0
    ep_tap_deletes:                                 4
    ep_tap_fg_fetched:                              6253096
    ep_tap_keepalive:                               600
    ep_tap_noop_interval:                           200
    ep_tap_total_fetched:                           6253106
    ep_tap_total_queue:                             0
    eq_tapq:xx.xx.xx.xx:11211:ack_log_size:        0
    eq_tapq:xx.xx.xx.xx:11211:ack_seqno:           7294
    eq_tapq:xx.xx.xx.xx:11211:ack_window_full:     false
    eq_tapq:xx.xx.xx.xx:11211:bg_backlog_size:     0
    eq_tapq:xx.xx.xx.xx:11211:bg_jobs_completed:   0
    eq_tapq:xx.xx.xx.xx:11211:bg_jobs_issued:      0
    eq_tapq:xx.xx.xx.xx:11211:bg_queue_size:       0
    eq_tapq:xx.xx.xx.xx:11211:bg_queued:           0
    eq_tapq:xx.xx.xx.xx:11211:bg_result_size:      0
    eq_tapq:xx.xx.xx.xx:11211:bg_results:          0
    eq_tapq:xx.xx.xx.xx:11211:bg_wait_for_results: false
    eq_tapq:xx.xx.xx.xx:11211:complete:            false
    eq_tapq:xx.xx.xx.xx:11211:connected:           true
    eq_tapq:xx.xx.xx.xx:11211:disconnects:         3
    eq_tapq:xx.xx.xx.xx:11211:empty:               true
    eq_tapq:xx.xx.xx.xx:11211:flags:               20
    eq_tapq:xx.xx.xx.xx:11211:has_item:            false
    eq_tapq:xx.xx.xx.xx:11211:has_queued_item:     false
    eq_tapq:xx.xx.xx.xx:11211:idle:                true
    eq_tapq:xx.xx.xx.xx:11211:paused:              true
    eq_tapq:xx.xx.xx.xx:11211:pending_backfill:    false
    eq_tapq:xx.xx.xx.xx:11211:pending_disconnect:  false
    eq_tapq:xx.xx.xx.xx:11211:qlen:                0
    eq_tapq:xx.xx.xx.xx:11211:qlen_high_pri:       0
    eq_tapq:xx.xx.xx.xx:11211:qlen_low_pri:        0
    eq_tapq:xx.xx.xx.xx:11211:rec_fetched:         6258772
    eq_tapq:xx.xx.xx.xx:11211:reconnects:          3
    eq_tapq:xx.xx.xx.xx:11211:recv_ack_seqno:      7293
    eq_tapq:xx.xx.xx.xx:11211:vb_filters:          1