utility refactoring and include fix

src/include/aes67/rtsp.h

src/include/aes67/utils/mdns.h

src/include/aes67/utils/rtsp-dsc.h

src/utils/rtsp-describe/CMakeLists.txt

src/utils/rtsp-describe/rtsp-describe.c

src/utils/rtsp-dsc.c

src/utils/sapd/CMakeLists.txt

src/utils/sapd/sapd.c