Persist SRVCC-related properties in GsmConnection

Makes sure that PROPERTY_IS_DOWNGRADED_CONFERENCE and
CAPABILITY_CONFERENCE_HAS_NO_CHILDREN are not erased when
updateConnectionProperties and updateConnectionCapabilities are called.

Bug: 29806833
Change-Id: Id8e3a81845df0bc144a040c68709db111f467473
2 files changed