vmxnet3: Don't enable vlan filters in promiscuous mode.

The vmxnet3 driver enables vlan filters if filtering is enabled for
any vlan.  In promiscuous mode the filter table is cleared to in
order to disable filtering.  However, if a vlan device is subsequently
created that vlan will be added to the filter, re-engaging it.  As a
result, not only do we not see all the vlans in promiscuous mode, we
don't even see vlans for which a filter was previously created.

CC: Scott J. Goldman <scottjg@vmware.com>
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: Shreyas N Bhatewara <sbhatewara@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>