ixgbe: fix tag stripping for VLAN ID 0

Register VLAN ID 0 so that frames with VLAN ID 0 are received and get
their tag stripped when ixgbe is not in DCB mode.  VLAN ID 0 means
that the frame is 'priority tagged' only - it is not a VLAN, but the
priority value is the tag in valid.  The functions
ixgbe_vlan_rx_register() and ixgbe_vlan_rx_kill_vid() were moved up a
couple functions to correct compiling issues with this change.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Eric W Multanen <eric.w.multanen@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>