net: dsa: tag_brcm: 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.

Cc: Florian Fainelli <f.fainelli@gmail.com>
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_brcm.c

@@ -66,9 +66,6 @@ static struct sk_buff *brcm_tag_xmit_ll(struct sk_buff *skb,
 	u16 queue = skb_get_queue_mapping(skb);
 	u8 *brcm_tag;
 
-	if (skb_cow_head(skb, BRCM_TAG_LEN) < 0)
-		return NULL;
-
 	/* The Ethernet switch we are interfaced with needs packets to be at
 	 * least 64 bytes (including FCS) otherwise they will be discarded when
 	 * they enter the switch port logic. When Broadcom tags are enabled, we