Use container_of() macro to get to timewait info structure instead of
typecasting.

Link: https://lore.kernel.org/r/20191002122517.17721-5-leon@kernel.orgSigned-off-by: NParav Pandit <parav@mellanox.com>
Signed-off-by: NLeon Romanovsky <leonro@mellanox.com>
Reviewed-by: NJason Gunthorpe <jgg@mellanox.com>
Signed-off-by: NJason Gunthorpe <jgg@mellanox.com>