IB/IPoIB: ndo_set_rx_mode_async conversion

IB/IPoIB: ndo_set_rx_mode_async conversion

The commit in the fixes tag added a warning for devices
that are netdev ops locked that they should be converted
to .ndo_set_rx_mode_async. IPoIB for mlx5 is such a
driver which was missed during the conversion because the
flow is more complex:
- mlx5 part of IPoIB device was converted to ops-lock in commit [1].
- ipoib_intf_init() then overrides netdev_ops with
  ipoib_netdev_ops_{pf,vf}, which still wired ndo_set_rx_mode to the
  legacy sync path -- tripping the new warning on every probe.

So now we have the following splat:
  netdevice: ib0 (uninitialized): ops-locked drivers should use ndo_set_rx_mode_async
  WARNING: net/core/dev.c:11366 at register_netdevice+0x83c/0x21d0
  ...
  register_netdev+0x1f/0x40
  ipoib_add_one+0x35c/0x880 [ib_ipoib]

This patch implements .ndo_set_rx_mode_async but it simply schedules the
multicast restart task like before. This is done to maintain the
assumption that this task and others [2] must run on the same order
workqueue to avoid racing with themselves. The race between
ipoib_mcast_join_task() and ipoib_mcast_restart_task() would be the most
obvious example.

[1] 8f7b00307bf1, "net/mlx5e: Convert mlx5 netdevs to instance locking")
[2] ipoib_mcast_join_task, ipoib_mcast_restart_task,
    ipoib_mcast_carrier_on_task, ipoib_reap_ah, ipoib_reap_neigh

Fixes: 3cbd22938877 ("net: warn ops-locked drivers still using ndo_set_rx_mode")
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://patch.msgid.link/20260513124519.3357165-1-dtatulea@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>