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/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@420434 f38db490-d61c-443f-a65b-d21fe96a405b