UPSTREAM: ipv6: fib: Unlink replaced routes from their nodes

When a route is deleted its node pointer is set to NULL to indicate it's
no longer linked to its node. Do the same for routes that are replaced.

This will later allow us to test if a route is still in the FIB by
checking its node pointer instead of its reference count.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Cherry-pick from: 7483cea79957312e9f8e9cf760a1bc5d6c507113
Bug: 64978549

Change-Id: Ibfa54cf918084138b6b19437e9ef86bfaea5deae

Author: idosch

net/ipv6/ip6_fib.c

@@ -909,6 +909,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 			fn->fn_flags |= RTN_RTINFO;
 		}
 		nsiblings = iter->rt6i_nsiblings;
+		iter->rt6i_node = NULL;
 		fib6_purge_rt(iter, fn, info->nl_net);
 		if (fn->rr_ptr == iter)
 			fn->rr_ptr = NULL;
@@ -923,6 +924,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct rt6_info *rt,
 					break;
 				if (rt6_qualify_for_ecmp(iter)) {
 					*ins = iter->dst.rt6_next;
+					iter->rt6i_node = NULL;
 					fib6_purge_rt(iter, fn, info->nl_net);
 					if (fn->rr_ptr == iter)
 						fn->rr_ptr = NULL;