【BLE】MTU config

手机端请求mtu， 设备端请求mtu为251

2021-04-21 11:44:38.114 15027-15027/com.example.paak.baonengtestapp I/BleConnectionManager: requestMtu: 255
2021-04-21 11:44:38.133 15027-15045/com.example.paak.baonengtestapp I/BleConnectionManager: onMtuChanged(): 251, status: 0

2021-04-21 11:20:56.820 14006-14006/com.example.paak.baonengtestapp I/BleConnectionManager: requestMtu: 200
2021-04-21 11:20:56.837 14006-14072/com.example.paak.baonengtestapp I/BleConnectionManager: onMtuChanged(): 200, status: 0

2021-04-21 10:11:39.338 7988-8888/com.example.paak.baonengtestapp I/BleConnectionManager: onMtuChanged(): 150, status: 0
2021-04-21 10:11:39.338 7988-8888/com.example.paak.baonengtestapp D/TransportProtocol: MtuObservable(): New MTU: 150