vdpa/mlx5: reuse common function for MAC address updates

vdpa/mlx5: reuse common function for MAC address updates

Factor out MAC address update logic and reuse it from handle_ctrl_mac().

This ensures that old MAC entries are removed from the MPFS table
before adding a new one and that the forwarding rules are updated
accordingly. If updating the flow table fails, the original MAC and
rules are restored as much as possible to keep the software and
hardware state consistent.

Signed-off-by: Cindy Lu <lulu@redhat.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20260126094848.9601-3-lulu@redhat.com>