drivers: net: xgene: Fix regression in CRC stripping

drivers: net: xgene: Fix regression in CRC stripping

All packets on ingress (except for jumbo) are terminated with a 4-bytes
CRC checksum. It's the responsability of the driver to strip those 4
bytes. Unfortunately a change dating back to March 2017 re-shuffled some
code and made the CRC stripping code effectively dead.

This change re-orders that part a bit such that the datalen is
immediately altered if needed.

Fixes: 4902a92270fb ("drivers: net: xgene: Add workaround for errata 10GE_8/ENET_11")
Cc: stable@vger.kernel.org
Signed-off-by: Stephane Graber <stgraber@ubuntu.com>
Tested-by: Stephane Graber <stgraber@ubuntu.com>
Link: https://lore.kernel.org/r/20220322224205.752795-1-stgraber@ubuntu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>