Allow mediaserver to connect to bluetooth.

Re-purpose the existing bluetooth_socket type, originally
for /dev/socket/bluetooth used by bluetoothd in the old
bluetooth stack, for sockets created by bluedroid under
/data/misc/bluedroid, and allow mediaserver to connect
to such sockets.  This is required for playing audio
on paired BT devices.

Based on b/12417855.

Change-Id: I24ecdf407d066e7c4939ed2a0edb97222a1879f6
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>