gre: raising the size of the buffer holding nl messages.

Now it matches the size for the answer defined in rtnl_talk()
and prevents stack corruption with answer > 1024 bytes.

ip/link_gre.c

@@ -53,7 +53,7 @@ static int gre_parse_opt(struct link_util *lu, int argc, char **argv,
 	struct {
 		struct nlmsghdr n;
 		struct ifinfomsg i;
-		char buf[1024];
+		char buf[16384];
 	} req;
 	struct ifinfomsg *ifi = (struct ifinfomsg *)(n + 1);
 	struct rtattr *tb[IFLA_MAX + 1];