cpu/native: add missing header in socket zep

Building e.g. gnrc_border_router example on FreeBSD fails due to
missing defines related to sockets. This adds the missing header
<sys/socket.h> to fix compiling.

cpu/native/socket_zep/socket_zep.c

@@ -21,6 +21,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/ioctl.h>
+#include <sys/socket.h>
 #include <sys/time.h>
 
 #include "async_read.h"