Fix IAX2 incoming call address lookups

This fixes address lookup for incoming calls without a peer definition.
The address family was unset instead of being set to AST_AF_UNSPEC
which was causing lookup failures on "127.0.0.1". This is one of the
causes of the current failure of the app_page integration test.

Review: https://reviewboard.asterisk.org/r/2933/
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Merged revisions 401291 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@401292 f38db490-d61c-443f-a65b-d21fe96a405b