[PATCH] forcedeth: decouple vlan and rx checksum dependency

This patch decouples the dependency between the rx checksum feature and
vlan feature. This is done by ignoring the checksum information if the
user has disabled rx checksum when vlan is enabled.

Signed-Off-By: Ayaz Abdulla <aabdulla@nvidia.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>