CBSE-1407: Adjust TCP recv parameter

Instead of hardcoded recv buffer size, Users can set recv_min_bytes
to adject tcp buffer size to improve througput performance

Change-Id: I299d55be93516c60fb3899aef8d2a1ad46f9423d
Reviewed-on: http://review.couchbase.org/42574
Reviewed-by: Bin Cui <bin.cui@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>