Bluetooth: Fix to avoid BluetoothPan ServiceConnection leak

Usecase:
1.) Make sure BT is turned off.
2.) Go to Settings -> Network & Internet
3.) Press back  from Network & Internet.
4.) Repeat above step 2000 times

Expected Result:
No ANR/Crashed should be seen.

Observed Result:
ServiceConnection leak is happening & android setting app get crashed.

Root cause: TetherPreferenceController tries to get
pan Proxy object, when BT is oFF, which is leaking one
service connection each time

Fix: getProfileProxy for Pan must only be called, when BT is
      turned on.

Test: lifeCycle_onCreate_shouldNotInitBluetoothPanWhenBluetoothOff

Bug: 79561076
Change-Id: I85208f48ce4dded94020cb156fcdb98b2cc873f9
Merged-In: I85208f48ce4dded94020cb156fcdb98b2cc873f9