The get_pai function in chan_sip.c didn't recognized a proper callerid name and

The get_pai function in chan_sip.c didn't recognized a proper callerid name and
 number from a P-Asserted-Identity cause the header parsing logic was wrong.
Changing the parsing functions to the sip header parsing APIs in
reqresp_parser.h solves this problem.

Review: https://reviewboard.asterisk.org/r/1673
Reviewed by: wdoekes2 and Mark Michelson
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Merged revisions 351396 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 351408 from http://svn.asterisk.org/svn/asterisk/branches/10

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@351409 65c4cc65-6c06-0410-ace0-fbb531ad65f3