[nrf fromtree] net: lib: coap_client: Drop duplicate MID only after responding with Ack

Even if we receive duplicate confirmable message, we should still
respond with the Ack. Just don't deliver the second callback.

This is achieved by moving the MID deduplication to after Ack handling.

Signed-off-by: Seppo Takalo <[email protected]>
(cherry picked from commit c0eb260)

Author: SeppoTakalo

subsys/net/lib/coap/coap_client.c

@@ -781,14 +781,6 @@ static int handle_response(struct coap_client *client, const struct coap_packet
 		return 0;
 	}
 
-	/* MID-based deduplication */
-	if (response_id == internal_req->last_response_id) {
-		LOG_WRN("Duplicate MID, dropping");
-		goto fail;
-	}
-
-	internal_req->last_response_id = response_id;
-
 	/* Received echo option */
 	if (find_echo_option(response, &client->echo_option)) {
 		 /* Resend request with echo option */
@@ -847,13 +839,21 @@ static int handle_response(struct coap_client *client, const struct coap_packet
 		}
 	}
 
+	/* MID-based deduplication */
+	if (response_id == internal_req->last_response_id) {
+		LOG_WRN("Duplicate MID, dropping");
+		return 0;
+	}
+
+	internal_req->last_response_id = response_id;
+
 	if (!internal_req->request_ongoing) {
 		if (internal_req->is_observe) {
 			(void) send_rst(client, response);
 			return 0;
 		}
 		LOG_DBG("Drop request, already handled");
-		goto fail;
+		return 0;
 	}
 
 	if (internal_req->pending.timeout != 0) {