Allow bluetooth to handle media_rw_data_file file descriptors
sent to it from other processes. Without this, bluetooth
picture / video sharing is broken.

Steps to reproduce:
1. Take few pictures
2. launch gallery and choose a picture/video and click on share and choose
   available BT device and share

Other info from bug report:

- Bluetooth process queries media content provider for a file descriptor,
  with an Uri like "content://media/external/images/media/69"
- Media server resolves the uri to a file on the filesystem, in the case of
  Gallery at "/storage/emulated/0/DCIM/Camera/IMG_20140128_141656.jpg"
- Media server returns the FD over binder to bluetooth
- Bluetooth is unable to read the file backed by the file descriptor.

Fixes Denial:

<5>[  821.040286] type=1400 audit(1390952161.805:11): avc:  denied  { read } for  pid=1348 comm="Binder_3" path="/data/media/0/DCIM/Camera/IMG_20140128_141656.jpg" dev="mmcblk0p23" ino=236246 scontext=u:r:bluetooth:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file

Bug: 12457805
Change-Id: I1423d06a98416ae4ab19508f0d005a6353acadc4