Follow error prone recommendation

```
In ObexServerSockets.java
51: warning: The field 'NUMBER_OF_SOCKET_TYPES' is never read.
    private static final int NUMBER_OF_SOCKET_TYPES = 2;
                             ^
68: warning: This update of a volatile variable is non-atomic
        mTag = "ObexServerSockets" + sInstanceCounter++;
                                                     ^
76: warning: The documented method doesn't actually throw this
     * @throws IOException if it occurs while creating the
       ^
89: warning: The documented method doesn't actually throw this
     * @throws IOException if it occurs while creating the
       ^
107: warning: The documented method doesn't actually throw this
     * @throws IOException if it occurs while creating the
       ^
140: warning: Method create() annotated [none] but too narrow;
invokes method requiring {allOf=[android.permission.BLUETOOTH_CONNECT]}
                l2capSocket = bt.listenUsingInsecureL2capOn(l2capPsm);
                                                                   ^
296: warning: A block tag has an empty description.
         * @throws IllegalArgumentException
           ^
295: warning: Parameter name `latch` is unknown.
         * @param latch shall never be null.
           ^
```

Bug: 236759221
Test: m RUN_ERROR_PRONE=true Bluetooth
Change-Id: I202c2f54e9aee1ba05b8035e8d17b5aa0854d987