i40e: fix MAC filters when removing VLANs

Currently there exists a bug where adding at least one VLAN and then
removing all VLANs leaves the mac filters for the VSI with an incorrect
value for 'vid' which indicates the mac filter's VLAN status.

The current implementation for handling the removal of VLANs is wrong
for a couple reasons. The first is that when i40e_vsi_kill_vlan
iterates through the MAC filters, it fails to account for the MAC filter
status; i.e. it's not accommodating for filters that are about to be
deleted. The second problem is that MAC filters can be deleted in other
places (specifically i40e_set_rx_mode). Thus if it occurs that all the
VLAN MAC filters get deleted we need to switch out of VLAN mode, but the
code path through i40e_vsi_kill_vlan has already been executed and we're
now stuck in VLAN mode.

This patch fixes the issue by removing the check from i40e_vsi_kill_vlan
and puts the check instead in i40e_sync_vsi_filters where we're
guaranteed to see all filter deletions and can properly detect when we
need to switch out of VLAN mode.

Change-ID: Ib38fe6034b356eee9a0e20b8a9eeed5ff2debcd9
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>