qlcnic: Add VXLAN Tx offload support

This patch adds LSO, LSO6 and Tx checksum offload support for VXLAN
encapsulated packets on 83xx/84xx series adapters.

Signed-off-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>