pch_gbe: vlan skb len fix

pch_gbe_xmit_frame skb->len verification was incorrect in vlan case
causing bogus transfer length errors.  One correction could be:
    offset = skb->protocol == htons(ETH_P_8021Q) ? 0 : 4;
    if (unlikely(skb->len > (adapter->hw.mac.max_frame_size - offset)))
However, this verification is not necessary, so remove it.

Signed-off-by: Andy Cress <andy.cress@us.kontron.com>
Signed-off-by: David S. Miller <davem@davemloft.net>