net/ipv6: Handle onlink flag with multipath routes

For multipath routes the ONLINK flag can be specified per nexthop in rtnh_flags or globally in rtm_flags. Update ip6_route_multipath_add to consider the ONLINK setting coming from rtnh_flags. Each loop over nexthops the config for the sibling route is initialized to the global config and then per nexthop settings overlayed. The flag is 'or'ed into fib6_config to handle the ONLINK flag coming from either rtm_flags or rtnh_flags.

---
v2
- updated commit message to reflect flag can be global or per-nexthop and both need to be handled

 net/ipv6/route.c | 1 +
 1 file changed, 1 insertion(+)

index b3c1137ad0b8..b0d5c64e1978 100644
@@ -4112,6 +4112,7 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 				r_cfg.fc_encap_type = nla_get_u16(nla);
 		}
 
+		r_cfg.fc_flags |= (rtnh->rtnh_flags & RTNH_F_ONLINK);
 		rt = ip6_route_info_create(&r_cfg, extack);
 		if (IS_ERR(rt)) {
 			err = PTR_ERR(rt);

2.11.0