net: stmmac: Prevent DSA tags from breaking COE

net: stmmac: Prevent DSA tags from breaking COE

Some DSA tagging protocols change the EtherType field in the MAC header
e.g.  DSA_TAG_PROTO_(DSA/EDSA/BRCM/MTK/RTL4C_A/SJA1105). On TX these tagged
frames are ignored by the checksum offload engine and IP header checker of
some stmmac cores.

On RX, the stmmac driver wrongly assumes that checksums have been computed
for these tagged packets, and sets CHECKSUM_UNNECESSARY.

Add an additional check in the stmmac TX and RX hotpaths so that COE is
deactivated for packets with ethertypes that will not trigger the COE and
IP header checks.

Fixes: 6b2c6e4a938f ("net: stmmac: propagate feature flags to vlan")
Cc:  <stable@vger.kernel.org>
Reported-by: Richard Tresidder <rtresidd@electromag.com.au>
Link: https://lore.kernel.org/netdev/e5c6c75f-2dfa-4e50-a1fb-6bf4cdb617c2@electromag.com.au/
Reported-by: Romain Gantois <romain.gantois@bootlin.com>
Link: https://lore.kernel.org/netdev/c57283ed-6b9b-b0e6-ee12-5655c1c54495@bootlin.com/
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>