vmxnet3: Remove incorrect implementation of ethtool_ops::get_flags()

Only some netdev feature flags correspond directly to ethtool feature
flags.  ethtool_op_get_flags() does the right thing.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Bhavesh Davda <bhavesh@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>