iavf: fix VLAN filter lost on add/delete race

When iavf_add_vlan() finds an existing filter in IAVF_VLAN_REMOVE
state, it transitions the filter to IAVF_VLAN_ACTIVE assuming the
pending delete can simply be cancelled. However, there is no guarantee
that iavf_del_vlans() has not already processed the delete AQ request
and removed the filter from the PF. In that case the filter remains in
the driver's list as IAVF_VLAN_ACTIVE but is no longer programmed on
the NIC. Since iavf_add_vlans() only picks up filters in
IAVF_VLAN_ADD state, the filter is never re-added, and spoof checking
drops all traffic for that VLAN.

  CPU0                       CPU1                     Workqueue
  ----                       ----                     ---------
  iavf_del_vlan(vlan 100)
    f->state = REMOVE
    schedule AQ_DEL_VLAN
                             iavf_add_vlan(vlan 100)
                               f->state = ACTIVE
                                                      iavf_del_vlans()
                                                        f is ACTIVE, skip
                                                      iavf_add_vlans()
                                                        f is ACTIVE, skip

  Filter is ACTIVE in driver but absent from NIC.

Transition to IAVF_VLAN_ADD instead and schedule
IAVF_FLAG_AQ_ADD_VLAN_FILTER so iavf_add_vlans() re-programs the
filter.  A duplicate add is idempotent on the PF.

Fixes: 0c0da0e95105 ("iavf: refactor VLAN filter states")

Signed-off-by: Petr Oros <poros@redhat.com>