RDMA/siw: Remove direct link to net_device

Do not manage a per device direct link to net_device. Rely
on associated ib_devices net_device management, not doubling
the effort locally. A badly managed local link to net_device
was causing a 'KASAN: slab-use-after-free' exception during
siw_query_port() call.

Fixes: bdcf26bf ("rdma/siw: network and RDMA core interface")
Reported-by:  <syzbot+4b87489410b4efd181bf@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=4b87489410b4efd181bf


Signed-off-by: Bernard Metzler <bmt@zurich.ibm.com>
Link: https://patch.msgid.link/20241212151848.564872-1-bmt@zurich.ibm.com


Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Leon Romanovsky <leon@kernel.org>