MB-11714: set TCP_NODELAY on our end of xdcr upr sockets

After removal of replies for window update requests we've started
hitting classical issue with combination of naggle and delayed
ack. Specifically after xdcr upr socket sees stream end it sends
window update request with maximal window size and puts socket back to
pool. It's possible that shortly after that socket is taken back and
used for upr-ing another vbucket which starts with stats requests. But
kernel at ep-engine side does delayed ack (anticipating some response
from applidation so that ack can be combined with app data). And lack
of ack triggers naggle on our end delaying stats request until ack for
previous segment (window update request) arrives.

TCP_NODELAY disables naggle and fixes the problem.

Change-Id: Ib659ff40701c0efb82ae7d6ee999bf15ae91e22a
Reviewed-on: http://review.couchbase.org/39419
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>