i40e: remove second check of VLAN_N_VID in i40e_vlan_rx_add_vid

Replace a check of magic number 4095 with VLAN_N_VID. This
makes it obvious that a later check against VLAN_N_VID is
always true and can be removed.

Change-ID: I28998f127a61a529480ce63d8a07e266f6c63b7b
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>