Fix compiler warning.
diff --git a/ripd/ripd.c b/ripd/ripd.c
index 6b79a16..acf0e7d 100644
--- a/ripd/ripd.c
+++ b/ripd/ripd.c
@@ -31,6 +31,7 @@
 #include "stream.h"
 #include "filter.h"
 #include "sockunion.h"
+#include "sockopt.h"
 #include "routemap.h"
 #include "if_rmap.h"
 #include "plist.h"