Properly invert the return of a strncmp call.

This was causing identification that should have been
made private to be public.

(closes issue AST-814)
reported by Patrick Anderson

Patches:
	chan_sip.c.diff uploaded by Patrick Anderson (license 5430)
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Merged revisions 355268 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 355271 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@355274 65c4cc65-6c06-0410-ace0-fbb531ad65f3