Fixes to the fd-oriented SIP TCP reads.
Don't crash on large user input. Allow SIP headers without space.
Optimize code a bit.
Review: https://reviewboard.asterisk.org/r/2162
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Merged revisions 375111 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 375112 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 375113 from http://svn.asterisk.org/svn/asterisk/branches/11
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@375114
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