Only do frame payload check for HOLD frames.

Only do frame payload check for HOLD frames.

This code was added for helping to debug the source of invalid HOLD frames.
However, a side effect of this is that it will incorrectly report errors for
frames that have an integer payload.  Make the check for this block specific
to the HOLD frame case.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@233092 65c4cc65-6c06-0410-ace0-fbb531ad65f3