IB/iser: Collapse cleanup and disconnect handlers

No real need to wait for TIMEWAIT_EXIT before we destroy the RDMA
resources (also TIMEAWAIT_EXIT is not guarenteed to always arrive).  As
for the cma_id, only destroy it if the state is not DOWN where in this
case, conn_release is already running and we don't want to compete.

Signed-off-by: Ariel Nahum <arieln@mellanox.com>
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>