Merge branch 'net-stmmac-fix-vlan-handling-when-interface-is-down'

Ovidiu Panait says:

====================
net: stmmac: Fix VLAN handling when interface is down

VLAN register accesses on the MAC side require the PHY RX clock to be
active. When the network interface is down, the PHY is suspended and
the RX clock is unavailable, causing VLAN operations to fail with
timeouts.

The VLAN core automatically removes VID 0 after the interface goes down
and re-adds it when it comes back up, so these timeouts happen during
normal interface down/up:

    # ip link set end1 down
    renesas-gbeth 15c40000.ethernet end1: Timeout accessing MAC_VLAN_Tag_Filter
    renesas-gbeth 15c40000.ethernet end1: failed to kill vid 0081/0

Adding VLANs while the interface is down also fails:

    # ip link add link end1 name end1.10 type vlan id 10
    renesas-gbeth 15c40000.ethernet end1: Timeout accessing MAC_VLAN_Tag_Filter
    RTNETLINK answers: Device or resource busy

Patch 4 fixes this by adding checks in the VLAN paths for netif_running(),
and skipping register accesses if the interface is down. Only the software
state is updated in this case. When the interface is brought up, the VLAN
state is restored to hardware.

Patches 1-3 fix some issues in the existing VLAN implementation.
====================

Link: https://patch.msgid.link/20260303145828.7845-1-ovidiu.panait.rb@renesas.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>