Tethering: add isTetheringSupported with callerPkg parameter

BT tethering need to know whether tethering is supported for its caller
that call isTetheringSupported in binder thread under BT's process.
Current isTetheringSupported API is getting callerPkg inside
TetheringManager that would be BT's package name for bt tethering case.
Provide isTetheringSupported(String callerPkg) for caller to pass its
caller's package name if the use case is under binder IPC.

Bug: 146915889
Test: -boot, flash, boot
Change-Id: I2a35e1b6851e7a799c343be0dd60da23514768ba