chan_sip: Replace sip_tls_read() and resolve the large SDP poll issue.

Replace sip_tls_read() and sip_tcp_read() with a single function and
resolve the poll/wait issue with large SDP payloads.

ASTERISK-18345 #close
Reported by: Stephane Chazelas
Patches:
      tcptls_pollv4.diff (license #5835) patch uploaded by Elazar Broad

Review: https://reviewboard.asterisk.org/r/3882/
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Merged revisions 420434 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 420435 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/certified/branches/11.6@420559 65c4cc65-6c06-0410-ace0-fbb531ad65f3