RDMA/siw: Remove NETDEV_GOING_DOWN event handler

RDMA/siw: Remove NETDEV_GOING_DOWN event handler

Toggling link while running NVME-oF over siw hits a kernel panic
due to race condition within siw_handler and ib_destroy_qp().
The IB_EVENT_PORT_ERR event can alone handle destroying qps.
therefore remove unwanted processing in siw.

Suggested-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Showrya M N <showrya@chelsio.com>
Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Link: https://lore.kernel.org/r/20240724085428.3813-1-showrya@chelsio.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>