net: dns: Close socket service properly from dispatcher

We need to close the socket service context when dispatcher is
unregistered.

Fixes #82652

Signed-off-by: Jukka Rissanen <[email protected]>
(cherry picked from commit da148ab)

Author: jukkar

subsys/net/lib/dns/dispatcher.c

@@ -334,6 +334,11 @@ int dns_dispatcher_unregister(struct dns_socket_dispatcher *ctx)
 
 	(void)sys_slist_find_and_remove(&sockets, &ctx->node);
 
+	(void)net_socket_service_unregister(ctx->svc);
+
+	/* Mark the context as unregistered */
+	ctx->sock = -1;
+
 	for (int i = 0; i < ctx->fds_len; i++) {
 		CHECKIF((int)ctx->fds[i].fd >= (int)ARRAY_SIZE(dispatch_table)) {
 			ret = -ERANGE;