Add missing back icon in action bar of Network Operator

Change-Id: I574557bb5cc91d24f17b9cc3a854a022c1ccadcb
PhoneApp: Initialize ToneGenerator when needed

Whenever there is a radio tech change, mSignalInfoToneGenerator
is released and never created. This leads to phone app crash later
when it is accessed for toneplay. This is fixed by creating the
instance (if null) before calling the APIs.

Bug: 8609102
Change-Id: Id9ebe6af5c1f92520ee5c2ca6efc4db335eb01f7