bluetooth: gatt: Fix ATT Read By Type by DB change unaware client

When change unaware client send ATT request it shall get Database
Out of Sync error. Reading GATT database hash is an exception here.

This was affecting GATT/SR/GAS/BV-05-C qualification test case.

Signed-off-by: Szymon Janc <szymon.janc@codecoup.pl>

subsys/bluetooth/host/att.c

@@ -1549,6 +1549,23 @@ static uint8_t att_read_type_req(struct bt_att_chan *chan, struct net_buf *buf)
 		return 0;
 	}
 
+	/* Reading Database Hash is special as it may be used to make client change aware
+	 * (Core Specification 5.4 Vol 3. Part G. 2.5.2.1 Robust Caching).
+	 *
+	 * GATT client shall always use GATT Read Using Characteristic UUID sub-procedure for
+	 * reading Database Hash
+	 * (Core Specification 5.4 Vol 3. Part G. 7.3 Databse Hash)
+	 */
+	if (bt_uuid_cmp(&u.uuid, BT_UUID_GATT_DB_HASH) != 0) {
+		if (!bt_gatt_change_aware(chan->att->conn, true)) {
+			if (!atomic_test_and_set_bit(chan->flags, ATT_OUT_OF_SYNC_SENT)) {
+				return BT_ATT_ERR_DB_OUT_OF_SYNC;
+			} else {
+				return 0;
+			}
+		}
+	}
+
 	return att_read_type_rsp(chan, &u.uuid, start_handle, end_handle);
 }