igb: Implement igb-specific oversize check

igb has a configurable size limit for LPE, and uses different limits
depending on whether the packet is treated as a VLAN packet.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Sriram Yagnaraman <sriram.yagnaraman@est.tech>
Signed-off-by: Jason Wang <jasowang@redhat.com>