net: stmmac: Consider Tx VLAN offload tag length for maxSDU

net: stmmac: Consider Tx VLAN offload tag length for maxSDU

Queue maxSDU requirement of 802.1 Qbv standard requires mac to drop
packets that exceeds maxSDU length and maxSDU doesn't include
preamble, destination and source address, or FCS but includes
ethernet type and VLAN header.

On hardware with Tx VLAN offload enabled, VLAN header length is not
included in the skb->len, when Tx VLAN offload is requested. This
leads to incorrect length checks and allows transmission of
oversized packets. Add the VLAN_HLEN to the skb->len before checking
the Qbv maxSDU if Tx VLAN offload is requested for the packet.

Fixes: c5c3e1bfc9e0 ("net: stmmac: Offload queueMaxSDU from tc-taprio")
Signed-off-by: Rohan G Thomas <rohan.g.thomas@altera.com>
Reviewed-by: Matthew Gerlach <matthew.gerlach@altera.com>
Link: https://patch.msgid.link/20251028-qbv-fixes-v4-2-26481c7634e3@altera.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>