zebra: fix fpm_listener compilation

I don't know why it appears only now.

> ../sdist/zebra/fpm_listener.c:420:8: error: comparison of integers of different signs: 'int' and 'size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
>                 if (!RTNH_OK(rtnh, len)) {
>                      ^~~~~~~~~~~~~~~~~~
> ../sdist/include/linux/rtnetlink.h:437:31: note: expanded from macro 'RTNH_OK'
>                            ((int)(rtnh)->rtnh_len) <= (len))

len is set with RTA_PAYLOAD and should be an integer.

> len = RTA_PAYLOAD(mpath_rtattr);
> #define RTA_PAYLOAD(rta) ((int)((rta)->rta_len) - RTA_LENGTH(0))

Signed-off-by: Louis Scalbert <[email protected]>

zebra/fpm_listener.c

@@ -405,7 +405,7 @@ static int netlink_msg_ctx_add_nh(struct netlink_msg_ctx *ctx, int if_index,
 static int parse_multipath_attr(struct netlink_msg_ctx *ctx,
 				struct rtattr *mpath_rtattr)
 {
-	size_t len;
+	int len;
 	struct rtnexthop *rtnh;
 	struct rtattr *rtattrs[RTA_MAX + 1];
 	struct rtattr *gateway;