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


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/12@405928 f38db490-d61c-443f-a65b-d21fe96a405b