Add Handover Failure Mode to Radio Hal

On a handover request failure, the modem can now determine
whether or not to fallback.  There is also the option to revert
to the legacy logic.  Following the legacy logic is the default
behavior.

Test: FrameworkTelephonyTests
Bug: 161572465
Change-Id: I194aca34131301a3507ad3ba99be278cbf6fa87b
Merged-In: I194aca34131301a3507ad3ba99be278cbf6fa87b