rtnetlink: Fix weight overflow in RTA_MULTIPATH

If the weight value is larger than 8 bits, set it to the maximum.
Also, only send RTA_WEIGHT if its value is not the default.
This reduces message size and matches the behavior of
non-multipath routes.

Reviewed by:	emaste, markj
Differential Revision: https://reviews.freebsd.org/D57266

sys/netlink/route/rt.c

@@ -217,7 +217,7 @@ dump_rc_nhg(struct nl_writer *nw, const struct route_nhop_data *rnd, struct rtms
 			return;
 		rtnh->rtnh_flags = 0;
 		rtnh->rtnh_ifindex = if_getindex(wn[i].nh->nh_ifp);
-		rtnh->rtnh_hops = wn[i].weight;
+		rtnh->rtnh_hops = MIN(wn[i].weight, UINT8_MAX);
 		dump_rc_nhop_gw(nw, wn[i].nh);
 		uint32_t rtflags = nhop_get_rtflags(wn[i].nh);
 		if (rtflags != base_rtflags)
@@ -242,7 +242,8 @@ dump_rc_nhg(struct nl_writer *nw, const struct route_nhop_data *rnd, struct rtms
 	}
 	nlattr_set_len(nw, off);
 	nlattr_add_u32(nw, NL_RTA_PRIORITY, nhop_metric);
-	nlattr_add_u32(nw, NL_RTA_WEIGHT, nhop_weight);
+	if (nhop_weight != RT_DEFAULT_WEIGHT)
+		nlattr_add_u32(nw, NL_RTA_WEIGHT, nhop_weight);
 }
 
 static void