This device claims TSO support for vlans.  It also allows a user to
control vlan acceleration offloading.  As such, it is possible to turn
off vlan acceleration and configure a vlan which will continue to send
TSO traffic.

In such situation the packet passed down the the device will contain
a vlan header and skb->protocol will be set to ETH_P_8021Q.
The device assumes that skb->protocol contains network protocol
value and uses that value to set up TSO information.
This results in corrupted frames sent on the wire.

This patch extracts the protocol value correctly by using a
vlan_get_protocol() helper and corrects corrupt TSO frames.

CC: Shahed Shaikh <shahed.shaikh@qlogic.com>
CC: Jitendra Kalsaria <jitendra.kalsaria@qlogic.com>
CC: Ron Mercer <ron.mercer@qlogic.com>
CC: linux-driver@qlogic.com
Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Acked-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>