iavf: add VIRTCHNL_OP_ADD_VLAN to success completion handler

The V1 ADD_VLAN opcode had no success handler; filters sent via V1
stayed in ADDING state permanently. Add a fallthrough case so V1
filters also transition ADDING -> ACTIVE on PF confirmation.

Critically, add an `if (v_retval) break` guard: the error switch in
iavf_virtchnl_completion() does NOT return after handling errors,
it falls through to the success switch. Without this guard, a
PF-rejected ADD would incorrectly mark ADDING filters as ACTIVE,
creating a driver/HW mismatch where the driver believes the filter
is installed but the PF never accepted it.

For V2, this is harmless: iavf_vlan_add_reject() in the error
block already kfree'd all ADDING filters, so the success handler
finds nothing to transition.

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-v1-4-cdcb48303fd8@intel.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>