net: dsa: tag_edsa: let DSA core deal with TX reallocation

Now that we have a central TX reallocation procedure that accounts for
the tagger's needed headroom in a generic way, we can remove the
skb_cow_head call.

Note that the VLAN code path needs a smaller extra headroom than the
regular EtherType DSA path. That isn't a problem, because this tagger
declares the larger tag length (8 bytes vs 4) as the protocol overhead,
so we are covered in both cases.

Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/dsa/tag_edsa.c

@@ -35,8 +35,6 @@ static struct sk_buff *edsa_xmit(struct sk_buff *skb, struct net_device *dev)
 	 * current ethertype field if the packet is untagged.
 	 */
 	if (skb->protocol == htons(ETH_P_8021Q)) {
-		if (skb_cow_head(skb, DSA_HLEN) < 0)
-			return NULL;
 		skb_push(skb, DSA_HLEN);
 
 		memmove(skb->data, skb->data + DSA_HLEN, 2 * ETH_ALEN);
@@ -60,8 +58,6 @@ static struct sk_buff *edsa_xmit(struct sk_buff *skb, struct net_device *dev)
 			edsa_header[6] &= ~0x10;
 		}
 	} else {
-		if (skb_cow_head(skb, EDSA_HLEN) < 0)
-			return NULL;
 		skb_push(skb, EDSA_HLEN);
 
 		memmove(skb->data, skb->data + EDSA_HLEN, 2 * ETH_ALEN);