net: vmxnet3: convert to hw_features

This also removes private feature flags that were always set to true.

You may want to move vmxnet3_set_features() to vmxnet3_drv.c as a following
cleanup.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>