kernel-netlink: Set usable state whenever an interface appears

If an interface is renamed we already have an entry (based on the
ifindex) allocated but previously only set the usable state once
based on the original name.

Fixes #2403.

src/libcharon/plugins/kernel_netlink/kernel_netlink_net.c

@@ -1183,13 +1183,13 @@ static void process_link(private_kernel_netlink_net_t *this,
 				INIT(entry,
 					.ifindex = msg->ifi_index,
 					.addrs = linked_list_create(),
-					.usable = charon->kernel->is_interface_usable(
-														charon->kernel, name),
 				);
 				this->ifaces->insert_last(this->ifaces, entry);
 			}
 			strncpy(entry->ifname, name, IFNAMSIZ);
 			entry->ifname[IFNAMSIZ-1] = '\0';
+			entry->usable = charon->kernel->is_interface_usable(charon->kernel,
+																name);
 			if (event && entry->usable)
 			{
 				if (!(entry->flags & IFF_UP) && (msg->ifi_flags & IFF_UP))