vmxnet3: turn off lro when rxcsum is disabled

Currently, when rx csum is disabled, vmxnet3 driver does not turn
off lro, which can cause performance issues if user does not turn off
lro explicitly. This patch adds fix_features support which is used to
turn off LRO whenever RXCSUM is disabled.

Signed-off-by: Ronak Doshi <doshir@vmware.com>
Acked-by: Rishi Mehta <rmehta@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>