vmxnet3: mimic Linux driver registration

vmxnet3 driver supplies information about its version and guest
OS to the device. The device (probably) uses this information
to enable or disable features accordingly.

Since we are going to use features absent in FreeBSD driver's
code we'd rather mimic Linux driver registration.

Reviewed-by: Takuya ASADA <syuu@cloudius-systems.com>
Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
vmxnet3: avoid excessive kicks on TX

There is a mechanism in vmxnet3 device that allows to decrease
number of device kicks on TX. This patch makes our driver use this feature.

Having this patch applied TX throughput improvement
of around 5% observed on small packets tests.

Reviewed-by: Takuya ASADA <syuu@cloudius-systems.com>
Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>