Changes

asterisk: extensions.conf: Allow extra MO call from SIP UA which HOLDed previous call

We need to keep track of the SIP UA using the IMS endpoint, so that when
the IMS call is set on HOLD we can identidy that the same SIP UA can
still initiate new calls on the IMS endpoint.

Related: SYS#7003
Change-Id: Idad9e613669466f3aac8b1c7b43f8d9b6e0494e6