chan_dahdi/PRI: Suppress CONNECTED_LINE updates when nothing in the udpate is valid.

* Also simplified some subddress handling code.

(closes issue ASTERISK-23008)
Reported by: Michael Cargile
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Merged revisions 405926 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 405927 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 405928 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@405947 65c4cc65-6c06-0410-ace0-fbb531ad65f3