Fix issue that Wifi Calling preference is showing wrong value.

When showing current Wifi Calling setting, we should decide
whether it's roaming based on telephony.isnetworkRoaming() instead
of checking the roaming button in setting page.

Bug: 67442943
Test: manual
Change-Id: I617cd4709a94ca888318e4903b0cdd2b00f3d84e
1 file changed