Check for P mode when in P4 (like F on others)

[chrissearle]

Seen from a log:

Unable to set virtual stick mode Error Domain=DJISDKMissionErrorDomain Code=-5000 "Cannot exectue in current mode. For products except Phantom 4, please make sure the remote controller's mode switch is in 'F' mode. For Phantom 4, please make sure the remote controller's mode switch is in 'P' mode. (code:-5000)" UserInfo={NSLocalizedDescription=Cannot exectue in current mode. For products except Phantom 4, please make sure the remote controller's mode switch is in 'F' mode. For Phantom 4, please make sure the remote controller's mode switch is in 'P' mode. (Code:-5000)}