Relax ACTION_TETHERING_STATE_CHANGED permissions.

This broadcast doesn't contain any sensitive BluetoothDevice extras;
it only contains a single boolean indicating tethering state, so
relax it to no longer require the BLUETOOTH_CONNECT permission.

Bug: 188706031
Test: atest BluetoothInstrumentationTests
Change-Id: Iab3be943d90b9a7042f897a07b828fbd890aa161