Check if the send buffer is full or not for an DCP mutation.

Change-Id: I4401cda9b16ced3278f505169ed1f4658e18dcfa
Reviewed-on: http://review.couchbase.org/40397
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>
Merge remote-tracking branch 'membase/3.0'

* membase/3.0:
  Check if the send buffer is full or not for an DCP mutation.

Change-Id: Ib58feb1f887f7b61918da429279e611f730c85c6