There are warnings when building test code

[hamishwillee]

ubuntu@ubuntu:~/github/cm/1test/camera-manager$ make test
make test/test-custom-stream test/test-rtsp-udp-stream-discovery test/test-camera-parameters test/test-mavlink-protocol
make[1]: Entering directory '/home/ubuntu/github/cm/1test/camera-manager'
  CXX      test/stream_builder_custom.o
  CXX      test/stream_custom.o
  CXXLD    test/test-custom-stream
  CXX      test/test_rtsp_udp_stream_discovery.o
  CXXLD    test/test-rtsp-udp-stream-discovery
  CXX      test/test_camera_parameters.o
  CXXLD    test/test-camera-parameters
  CXX      test/test_mavlink_protocol.o
test/test_mavlink_protocol.cpp: In function ‘void* discovercam(void*)’:
test/test_mavlink_protocol.cpp:274:7: warning: no previous declaration for ‘void* discovercam(void*)’ [-Wmissing-declarations]
 void *discovercam(void *cntx)
       ^
test/test_mavlink_protocol.cpp:282:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
test/test_mavlink_protocol.cpp: In member function ‘std::vector<int> Drone::getCameraIdList() const’:
test/test_mavlink_protocol.cpp:98:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
test/test_mavlink_protocol.cpp: In member function ‘int Drone::getMode(int)’:
test/test_mavlink_protocol.cpp:173:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
  CXXLD    test/test-mavlink-protocol
make[1]: Leaving directory '/home/ubuntu/github/cm/1test/camera-manager'