[LIBNFNETLINK] Add NLMSG_OK checking to nfnl_get_msg_next

nfnl_get_msg_next must check is the message is OK after NLMSG_NEXT
is called.

Index: libnfnetlink/src/libnfnetlink.c
===================================================================
--- libnfnetlink.orig/src/libnfnetlink.c	2006-02-12 19:24:26.000000000 +0100
+++ libnfnetlink/src/libnfnetlink.c	2006-02-12 19:28:19.000000000 +0100
@@ -861,6 +861,11 @@ struct nlmsghdr *nfnl_get_msg_next(struc
 	remain_len = (len - ((unsigned char *)h->last_nlhdr - buf));
 	nlh = NLMSG_NEXT(h->last_nlhdr, remain_len);
 
+	if (!NLMSG_OK(nlh, remain_len)) {
+		h->last_nlhdr = NULL;
+		return NULL;
+	}
+
 	h->last_nlhdr = nlh;
 
 	return nlh;