chan_sip: trust_id_outbound CHANGES message improvement

(closes issue AST-1301)

(closes issue ASTERISK-19465)
Reported by: Krzysztof Chmielewski
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Merged revisions 412821 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 412822 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 412823 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@412824 65c4cc65-6c06-0410-ace0-fbb531ad65f3