Allow bluetooth access to the tun device.

Bluetooth uses the tun device for tethering. Allow access.

  STEPS TO REPRODUCE:
  0. Have two devices to test on, say Device A and Device B
  1. On Device A, Go to settings ->Bluetooth .
  2. Turn on the Bluetooth .
  3. Pair it with device B
  4. Tap on the paired device

  OBSERVED RESULTS:
  -Bluetooth share crash is observed with "Bluetooth share has stopped"
  error message
  -Unable to use Bluetooth tethering due to this issue

  EXPECTED RESULTS:
  No crash and Bluetooth devices should be able to connect for tethering

Addresses the following denial:

com.android.bluetooth: type=1400 audit(0.0:131): avc: denied { open }
for comm=425420536572766963652043616C6C path="/dev/tun" dev="tmpfs"
ino=12340 scontext=u:r:bluetooth:s0 tcontext=u:object_r:tun_device:s0
tclass=chr_file permissive=0

Bug: 27372573
Change-Id: I07724d8d68ffcdda691f1179787a4f40a0ab1c73