Fix domain selection while in ECBM on PS cellular

Route the dialing request to IMS if the ePDN connection
has been connected over PS cellular in emergency callback mode,
instead of scanning cellular networks.

Bug: 319348395
Test: atest EmergencyCallDomainSelectorTest
Change-Id: I5c8557ebc65497aaf5bff244aabb83482e64902f
3 files changed