res_rtp_asterisk: Ensure that the base and mapped address for candidates is present...

res_rtp_asterisk: Ensure that the base and mapped address for candidates is present in SDP.

This change fixes an issue where ICE candidates put into the SDP did not contain
the 'raddr' and 'rport' information for server reflexive and relay candidates.

#SIPit31
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Merged revisions 424151 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 424152 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 424153 from http://svn.asterisk.org/svn/asterisk/branches/13

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@424154 65c4cc65-6c06-0410-ace0-fbb531ad65f3