MB-11439: added xmem replies to xdcr trace

Change-Id: I3f634edcc5d565be96f9b2a6001bec9cada01052
Reviewed-on: http://review.couchbase.org/38728
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>