hnbgw: Allow announcing a different mgw-local IuUP address after MDCX

This will allow emulating an MGW deciding to change its local IuUP IP
address due to received remote address in MGCP MDCX, and announce the
changed address back in MGCP MDCX. A test validating this scenario
against osmo-hnbgw will be added in a follow-up patch.

Related: SYS#6657
Change-Id: Ia724e0363a8bab56f5d31e7f7f7a127af584f935
1 file changed