UNICAST max_xmit_req_size doesn't work

UNICAST3 sets max_xmit_req_size to avoid requesting too many messages to fit into the maximum message size.
But the check is implemented incorrectly, so it is not effective.

JGRP000029: node1: failed sending message to node2 (120314 bytes): java.io.IOException: Message too long, headers: UNICAST3: XMIT_REQ, seqno=0, TP: [cluster_name=cluster]