atl1: fix frame length bug

The driver sets up the hardware to accept a frame with max length
equal to MTU + Ethernet header + FCS + VLAN tag, but we neglect to
add the VLAN tag size to the ingress buffer.  When a VLAN-tagged
frame arrives, the hardware passes it, but bad things happen
because the buffer is too small.  This patch fixes that.

Thanks to David Harris for reporting the bug and testing the fix.

Tested-by: David Harris <david.harris@cpni-inc.com>
Signed-off-by: Jay Cliburn <jacliburn@bellsouth.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>