res_pjsip: Apply AOR outbound proxy to static contacts.

The outbound proxy for an AOR was not being applied to
any statically configured Contacts. This resulted in the
OPTIONS requests being sent to the wrong target.

This change sets the outbound proxy on statically configured
contacts once the AOR configuration is done being
applied.

ASTERISK-28965

Change-Id: Ia60f3e93ea63f819c5a46bc8b54be2e588dfa9e0