callerid: Logic error in checksum processing

Callerid checksum-ing was being handled incorrectly here. When the checksum is
calculated to be 0x00, it will perform 0x100-0x00 which results in 0x100. This
value will then fail the otherwise correct callerid message.

This patch changes the logic to simply add the calculated checksum to the
transmitted 2's compliment checksum.  

Review: https://reviewboard.asterisk.org/r/3356/
(closes issue ASTERISK-23488)

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This is a merge of merged revisions 410750 410747 from http://svn.asterisk.org/svn/asterisk/branches/12
I didn't want a broken patch to be comitted to trunk so I pre-merge merged them.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@410775 f38db490-d61c-443f-a65b-d21fe96a405b
res_pjsip_multihomed: Make address replacement less aggressive.

This change makes the res_pjsip_multihomed module less aggressive when
changing the address in messages. It will now only occur if the transport
in use is bound to the any address OR if the system determined source
address matches the bound address of the transport in use.

Review: https://reviewboard.asterisk.org/r/3369/
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Merged revisions 410793 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@410794 f38db490-d61c-443f-a65b-d21fe96a405b
res_pjsip: Enable PJSIP DNS client support.

This change enables DNS client support within PJSIP. System
nameservers are automatically discovered using res_init or
res_ninit. If this fails then PJSIP will resort to using
gethostbyname for resolution.

By enabling this support we gain SRV support, failover, and
weight support.

(closes issue ASTERISK-23435)
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/3343/
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Merged revisions 410795 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@410796 f38db490-d61c-443f-a65b-d21fe96a405b