CBSE-335: Retry withsocket.error on send()

Need to leverage the outer retry logic when failing to send ack msg

Change-Id: I4ed4b7c1e2b8f4b287e54b492db3ee82da8fb871
Reviewed-on: http://review.couchbase.org/24173
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Steve Yen <steve.yen@gmail.com>