fix build on OpenBSD

Fix the following build error:
 src/user_types/user_ipv4.c:29:19:
 error: use of undeclared identifier 'AF_INET'
     if (inet_pton(AF_INET, value_str, value->ptr) != 1) {

Signed-off-by: Renato Westphal <[email protected]>

Author: rwestphal

src/user_types/user_ipv4.c

@@ -15,6 +15,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <arpa/inet.h>
+#include <sys/socket.h>
 
 #include "../user_types.h"