Include lots of header files, rather than relying on O/S specific ones.

options.c

@@ -10,8 +10,9 @@
 #include <stdlib.h>
 #include <unistd.h>
 
-#include <net/if.h>
 #include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <net/if.h>
 
 #include "iftop.h"
 #include "options.h"