public int getConnectionState (BluetoothDevice device, int profile)

得到 远程设备profile的 连接状态
profile 为 GATT 或者 GATT_SERVER

返回值为：
STATE_DISCONNECTED = 0
STATE_CONNECTING = 1
STATE_CONNECTED = 2
STATE_DISCONNECTING = 3

BluetoothAdapter.getProfileConnectionState(int profile)
profile只能为 BluetoothProfile#HEADSET 或者 BluetoothProfile#A2DP.

    @SuppressLint("MissingPermission")
    public boolean isConnected() {
        if(mBluetoothGatt != null) {
             int state = mBluetoothManager.getConnectionState(mBluetoothGatt.getDevice(),  BluetoothProfile.GATT);
             return state == BluetoothProfile.STATE_CONNECTED;
        }
        return false;
    }