contrib

Add PJNATH patch that modifies the following behaviors:

 - "Local preference" used to compute the candidate priority is
 now unique to each candidate (i.e., two candidates of the same
 type will never have the same priority.)

 - The "nominated pair" selected by the controlling agent will be
 the active pair, regardless of the computed priority.

 - The permissions, given to peer candidates on TURN server when
 ICE negotiation starts, are now set permanent (periodically
 renewed) to allow a peer to send on any valid pairs (pairs that
 have successfully passed the connectivity checks.)

IMPORTANT: The patches are a back-port from PJSIP/PJNATH project,
these patches must be disabled when PSIP/PJNATH is upgraded.

Gitlab: #223
Change-Id: I82482d7da0b51f6e557fb6a5e98631f8b8a54db1