MB-11110: read option recv_min_bytes from extras

Change-Id: I31c86a5ee27f61f7522250e61d44a3203bc1bff0
Reviewed-on: http://review.couchbase.org/37046
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Reviewed-by: Daniel Owen <owend@couchbase.com>
Tested-by: Bin Cui <bin.cui@gmail.com>