Tbs: Set default technology bearer to GSM

This is used only when there is no call and no bearer is registered.
Also, in this patch we add mapping from TelephonyManager network types
to the Bluetooth Bearer Technology values from Bluetooth Assigned
Numbers.

Bug: 233335655
Test: atest BluetoothInstrumentationTests
Tag: #feature

Change-Id: Ieeff9d05e2e746e96d91c1ca225887b46e52fbb7