Bluetooth: ATT: Fix handling to EATT channels

EATT channels use bt_l2cap_chan_send which does return the number of
bytes sent on success not 0 as bt_l2cap_send.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

subsys/bluetooth/host/att.c

@@ -154,6 +154,8 @@ static int chan_send(struct bt_att_chan *chan, struct net_buf *buf,
 
 	if (IS_ENABLED(CONFIG_BT_EATT) &&
 	    atomic_test_bit(chan->flags, ATT_ENHANCED)) {
+		int err;
+
 		/* Check if sent is pending already, if it does it cannot be
 		 * modified so the operation will need to be queued.
 		 */
@@ -174,7 +176,15 @@ static int chan_send(struct bt_att_chan *chan, struct net_buf *buf,
 			return -EAGAIN;
 		}
 
-		return bt_l2cap_chan_send(&chan->chan.chan, buf);
+		/* bt_l2cap_chan_send does actually return the number of bytes
+		 * that could be sent immediatelly.
+		 */
+		err = bt_l2cap_chan_send(&chan->chan.chan, buf);
+		if (err < 0) {
+			return err;
+		}
+
+		return 0;
 	}
 
 	if (hdr->code == BT_ATT_OP_SIGNED_WRITE_CMD) {
@@ -233,7 +243,7 @@ static int chan_req_send(struct bt_att_chan *chan, struct bt_att_req *req)
 
 	/* Keep a reference for resending in case of an error */
 	err = chan_send(chan, net_buf_ref(req->buf), NULL);
-	if (err < 0) {
+	if (err) {
 		net_buf_unref(req->buf);
 		chan->req = NULL;
 	}