Disable VLAN pruning when entering promiscuous mode, and re-enable it
when exiting.

Without this VLAN-over-bridge topologies created on the device won't be
functional unless rx-vlan-filter is explicitly disabled with ethtool.
Signed-off-by: Nick Nunley <nicholas.d.nunley@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>