How to enable RTK in MSDK V4?

Network RTK：

1. Make sure you have added com.dji:library-networkrtk-helper:2.0.2 in build.gradle file.
2. Login DJI account.
3. setReferenceStationSource, set source as NETWORK_RTK，CMCC RTK set source as NTRIP_NETWORK_SERVICE.
4. setNetworkServiceCoordinateSystem, set navigation co-ordinate system，it is invaild for CMCC RTK.
5. setRtkEnabled, enable RTK service.
6. startNetworkService, start network RTK service，CMCC RTK should pass navigation co-ordinate system in the startNetworkService function.
7. addNetworkServiceStateCallback, add a listener to listen the network RTK state.
8. If NetworkServiceState.getChannelState is TRANSMITTING, it means the network RTK service has started.

Custom network RTK：

1. Make sure you have added com.dji:library-networkrtk-helper:2.0.2 in build.gradle file.
2. setReferenceStationSource, set source as CUSTOM_NETWORK_SERVICE.
3. setCustomNetworkSettings, set the custom network user configuration.
4. setRtkEnabled, enable RTK service.
5. startNetworkService, start network RTK service.
6. addNetworkServiceStateCallback, add a listener to listen the network RTK state.
7. If NetworkServiceState.getChannelState is TRANSMITTING, it means the network RTK service has started.

BASE_STATION：

1. setReferenceStationSource, set source as BASE_STATION.
2. If the aircraft is P4R, you need to call startMultiDevicePairing to pair up with the base station.
   
3. If the aircraft is M300, you need to setRtkBaseStationListCallback to register a callback for base station list, then call startSearchBaseStation to start searching the base station. When there is a base station occur, the setRtkBaseStationListCallback will return a callback. You can get base station ID and call connectToBaseStation to connect with base station.
   
4. setRtkEnabled, enable RTK service.

Tips：4.17-a1 version supports CMCC RTK.