avformat/unix: include sys/socket.h

unbreak android ndk r8 build
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/unix.c

@@ -26,6 +26,7 @@
  *
  */
 
+#include <sys/socket.h>
 #include <sys/un.h>
 
 #include "libavutil/avstring.h"