deciding whether or not we need to request retransmissions by sending a VNAK.
This code could cause VNAKs to be sent erroneously in some cases, and to not
be sent in other cases when it should have been.
(closes issue #10237, reported and patched by mihai)
git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.2@75927 65c4cc65-6c06-0410-ace0-fbb531ad65f3