iavf: wait for PF confirmation before removing VLAN filters

iavf: wait for PF confirmation before removing VLAN filters

The VLAN filter DELETE path was asymmetric with the ADD path: ADD
waits for PF confirmation (ADD -> ADDING -> ACTIVE), but DELETE
immediately frees the filter struct after sending the DEL message
without waiting for the PF response.

This is problematic because:
 - If the PF rejects the DEL, the filter remains in HW but the driver
   has already freed the tracking structure, losing sync.
 - Race conditions between DEL pending and other operations
   (add, reset) cannot be properly resolved if the filter struct
   is already gone.

Add IAVF_VLAN_REMOVING state to make the DELETE path symmetric:

  REMOVE -> REMOVING (send DEL) -> PF confirms -> kfree
                                -> PF rejects  -> ACTIVE

In iavf_del_vlans(), transition filters from REMOVE to REMOVING
instead of immediately freeing them. The new DEL completion handler
in iavf_virtchnl_completion() frees filters on success or reverts
them to ACTIVE on error.

Update iavf_add_vlan() to handle the REMOVING state: if a DEL is
pending and the user re-adds the same VLAN, queue it for ADD so
it gets re-programmed after the PF processes the DEL.

The !VLAN_FILTERING_ALLOWED early-exit path still frees filters
directly since no PF message is sent in that case.

Also update iavf_del_vlan() to skip filters already in REMOVING
state: DEL has been sent to PF and the completion handler will
free the filter when PF confirms. Without this guard, the sequence
DEL(pending) -> user-del -> second DEL could cause the PF to return
an error for the second DEL (filter already gone), causing the
completion handler to incorrectly revert a deleted filter back to
ACTIVE.

Fixes: 968996c070ef ("iavf: Fix VLAN_V2 addition/rejection")
Signed-off-by: Petr Oros <poros@redhat.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260427-jk-iwl-net-petr-oros-fixes-v1-3-cdcb48303fd8@intel.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>