zebra: Fix resetting valid flags for NHG dependents

Upon if_down, we don't reset the valid flag for dependents
and unset the INSTALLED flag.

So when its time for the NHG to be deleted (routes dereferenced),
zebra deletes it since refcnt goes to 0, but stale NHG remains in kernel.

Ticket :#4200788

Signed-off-by: Donald Sharp <sharpd@nvidia.com>

Signed-off-by: Rajasekar Raja <rajasekarr@nvidia.com>

zebra/zebra_nhg.c

@@ -1056,6 +1056,7 @@ static struct nhg_ctx *nhg_ctx_init(uint32_t id, struct nexthop *nh, struct nh_g
 static void zebra_nhg_set_valid(struct nhg_hash_entry *nhe, bool valid)
 {
 	struct nhg_connected *rb_node_dep;
+	bool dependent_valid = valid;
 
 	if (valid)
 		SET_FLAG(nhe->flags, NEXTHOP_GROUP_VALID);
@@ -1071,6 +1072,7 @@ static void zebra_nhg_set_valid(struct nhg_hash_entry *nhe, bool valid)
 
 	/* Update validity of nexthops depending on it */
 	frr_each (nhg_connected_tree, &nhe->nhg_dependents, rb_node_dep) {
+		dependent_valid = valid;
 		if (!valid) {
 			/*
 			 * Grab the first nexthop from the depending nexthop group
@@ -1080,16 +1082,22 @@ static void zebra_nhg_set_valid(struct nhg_hash_entry *nhe, bool valid)
 			struct nexthop *nexthop = rb_node_dep->nhe->nhg.nexthop;
 
 			while (nexthop) {
-				if (nexthop_same(nexthop, nhe->nhg.nexthop))
-					break;
-
+				if (nexthop_same(nexthop, nhe->nhg.nexthop)) {
+					/* Invalid Nexthop */
+					UNSET_FLAG(nexthop->flags, NEXTHOP_FLAG_ACTIVE);
+				} else {
+					/*
+					 * If other nexthops in the nexthop
+					 * group are valid then we can continue
+					 * to use this nexthop group as valid
+					 */
+					if (CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_ACTIVE))
+						dependent_valid = true;
+				}
 				nexthop = nexthop->next;
 			}
-
-			if (nexthop)
-				UNSET_FLAG(nexthop->flags, NEXTHOP_FLAG_ACTIVE);
 		}
-		zebra_nhg_set_valid(rb_node_dep->nhe, valid);
+		zebra_nhg_set_valid(rb_node_dep->nhe, dependent_valid);
 	}
 }