chan_sip: Use pvt outgoing_call variable to set Remote-Party-ID Header

Previously the pvt SIP_OUTGOING flag was used instead, which will frequently
flip during reinvites.

(closes issue AST-897)
Reported by: Thomas Arimont
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Merged revisions 371357 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371358 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 371382 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371383 65c4cc65-6c06-0410-ace0-fbb531ad65f3