vmxnet3: Convert to new vlan model.

This converts the vmxnet3 driver to use the new vlan model.  In doing so
it fixes missing tags in tcpdump and failure to do checksum offload when
tx vlan offload is disabled.

CC: Shreyas Bhatewara <sbhatewara@vmware.com>
CC: VMware PV-Drivers <pv-drivers@vmware.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: Scott J. Goldman <scottjg@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>