[MonoPosixHelper] Fix compilation for Android.

The Android NDK decalres the `struct timeval` struct in <sys/time.h>.
Update sys-socket.c to #include <sys/time.h> to fix compilation
with the Android NDK.

support/sys-socket.c

@@ -8,6 +8,7 @@
  */
 
 #include <sys/socket.h>
+#include <sys/time.h>
 #include <netinet/in.h>
 #include <sys/un.h>