net: if: Setup DAD timer regardless of DAD query result

In rare occasions when sending DAD NS packet fails, we should still
setup the DAD timer, unless we implement some kind of more advanced
retry mechanism. If we don't do that, the IPv6 address added to the
interface will never be usable in such cases.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
(cherry picked from commit 008a7ca)

subsys/net/ip/net_if.c

@@ -1295,21 +1295,25 @@ void net_if_ipv6_start_dad(struct net_if *iface,
 
 		ifaddr->dad_count = 1U;
 
-		if (!net_ipv6_start_dad(iface, ifaddr)) {
-			ifaddr->dad_start = k_uptime_get_32();
-			ifaddr->ifindex = net_if_get_by_iface(iface);
-
-			k_mutex_lock(&lock, K_FOREVER);
-			sys_slist_find_and_remove(&active_dad_timers,
-						  &ifaddr->dad_node);
-			sys_slist_append(&active_dad_timers, &ifaddr->dad_node);
-			k_mutex_unlock(&lock);
-
-			/* FUTURE: use schedule, not reschedule. */
-			if (!k_work_delayable_remaining_get(&dad_timer)) {
-				k_work_reschedule(&dad_timer,
-						  K_MSEC(DAD_TIMEOUT));
-			}
+		if (net_ipv6_start_dad(iface, ifaddr) != 0) {
+			NET_ERR("Interface %p failed to send DAD query for %s",
+				iface,
+				net_sprint_ipv6_addr(&ifaddr->address.in6_addr));
+		}
+
+		ifaddr->dad_start = k_uptime_get_32();
+		ifaddr->ifindex = net_if_get_by_iface(iface);
+
+		k_mutex_lock(&lock, K_FOREVER);
+		sys_slist_find_and_remove(&active_dad_timers,
+					  &ifaddr->dad_node);
+		sys_slist_append(&active_dad_timers, &ifaddr->dad_node);
+		k_mutex_unlock(&lock);
+
+		/* FUTURE: use schedule, not reschedule. */
+		if (!k_work_delayable_remaining_get(&dad_timer)) {
+			k_work_reschedule(&dad_timer,
+					  K_MSEC(DAD_TIMEOUT));
 		}
 	} else {
 		NET_DBG("Interface %p is down, starting DAD for %s later.",