net: mac802154: Save a global error code on transmissions

So far no error is returned from a failing transmission. However it
might sometimes be useful, and particularly easy to use during sync
transfers (for certain MLME commands). Let's create an internal variable
for that, global to the device. Right now only success are registered,
which is rather useless, but soon we will have more situations filling
this field.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20220407100903.1695973-4-miquel.raynal@bootlin.comSigned-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

net/mac802154/ieee802154_i.h

@@ -56,6 +56,8 @@ struct ieee802154_local {
 
 	struct sk_buff *tx_skb;
 	struct work_struct tx_work;
+	/* A negative Linux error code or a null/positive MLME error status */
+	int tx_result;
 };
 
 enum {

net/mac802154/util.c

@@ -58,8 +58,11 @@ enum hrtimer_restart ieee802154_xmit_ifs_timer(struct hrtimer *timer)
 void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb,
 			      bool ifs_handling)
 {
-	if (ifs_handling) {
 	struct ieee802154_local *local = hw_to_local(hw);
+
+	local->tx_result = IEEE802154_SUCCESS;
+
+	if (ifs_handling) {
 		u8 max_sifs_size;
 
 		/* If transceiver sets CRC on his own we need to use lifs