fix android ndk compile error, app crash when call pthread_join

[hongsunmin]

android ndk17+ compile error

SockCommon.cpp: error: no viable overloaded '=' imr.imr_multiaddr = groupAddress; imr.imr_sourceaddr = sourceFilterAddr; imr.imr_interface = INADDR_ANY;

When calling android rtspClient -> closeURL(idx), app crash occurs in pthread_join. After changing pthread_join to pthread_detach, the pthread is terminated and the app crash is resolved.