BugLink: https://bugs.launchpad.net/bugs/1801900

[ Upstream commit 35f3625c ]

When offloading the L3 and L4 csum computation on TX, we need to extract
the l3_proto from the ethtype, independently of the presence of a vlan
tag.

The actual driver uses skb->protocol as-is, resulting in packets with
the wrong L4 checksum being sent when there's a vlan tag in the packet
header and checksum offloading is enabled.

This commit makes use of vlan_protocol_get() to get the correct ethtype
regardless the presence of a vlan tag.

Fixes: 3f518509 ("ethernet: Add new driver for Marvell Armada 375 network unit")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>