vmxnet3: update to version 6

With all vmxnet3 version 6 changes incorporated in the vmxnet3 driver,
the driver can configure emulation to run at vmxnet3 version 6, provided
the emulation advertises support for version 6.

Signed-off-by: Ronak Doshi <doshir@vmware.com>
Acked-by: Guolin Yang <gyang@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>