Fix MAP accept threads sometimes spinning endlessly.

Randomly (under no obvious precondition), the MAP access threads spinned
endlessly after enabling BT, because mServerSocket.accept() always threw
IOExceptions, probably because the actual socket was already closed.
This change makes sure to exit the thread when that happens to not waste
CPU cycles and battery power.
This tracks similar changes done to the BluetoothPbapService and makes
sure to follow the (working) PBAP flow.

Change-Id: Iade905f0ea8829cce9666ddaebee7a8fd01f62b0