net: dsa: tag_brcm: legacy: fix pskb_may_pull length

BRCM_LEG_PORT_ID was incorrectly used for pskb_may_pull length.
The correct check is BRCM_LEG_TAG_LEN + VLAN_HLEN, or 10 bytes.

Fixes: 964dbf1 ("net: dsa: tag_brcm: add support for legacy tags")
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250529124406.2513779-1-noltari@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Noltari

net/dsa/tag_brcm.c

@@ -257,7 +257,7 @@ static struct sk_buff *brcm_leg_tag_rcv(struct sk_buff *skb,
 	int source_port;
 	u8 *brcm_tag;
 
-	if (unlikely(!pskb_may_pull(skb, BRCM_LEG_PORT_ID)))
+	if (unlikely(!pskb_may_pull(skb, BRCM_LEG_TAG_LEN + VLAN_HLEN)))
 		return NULL;
 
 	brcm_tag = dsa_etype_header_pos_rx(skb);