Fixed ANR during boot up

During boot up when IMS service is not up, when tons of network
requests arrive, each IMS reg technology retrieval would take
50ms. Because phone switcher is running on the main thread, those
requests during boot up block the main thread, then the phone
process does not have a chance to process the broadcast thus ANR
happens.

Fixed by not getting IMS reg technology when the device is not on
voice call, which is the case during boot up.

No logic was changed.

Fix: 365489613
Test: Basic telephony functionality tests
Test: atest FrameworksTelephonyTests
Flag: EXEMPT bug fix
Change-Id: Ib0ee30dec094a968e18736b48bc944c4790cc6db