RDMA/cm: Make sure the cm_id is in the IB_CM_IDLE state in destroy

RDMA/cm: Make sure the cm_id is in the IB_CM_IDLE state in destroy

The first switch statement in cm_destroy_id() tries to move the ID to
either IB_CM_IDLE or IB_CM_TIMEWAIT. Both states will block concurrent
MAD handlers from progressing.

Previous patches removed the unreliably lock/unlock sequences in this
flow, this patch removes the extra locking steps and adds the missing
parts to guarantee that destroy reaches IB_CM_IDLE. There is no point in
leaving the ID in the IB_CM_TIMEWAIT state the memory about to be kfreed.

Rework things to hold the lock across all the state transitions and
directly assert when done that it ended up in IB_CM_IDLE as expected.

This was accompanied by a careful audit of all the state transitions here,
which generally did end up in IDLE on their success and non-racy paths.

Link: https://lore.kernel.org/r/20200310092545.251365-16-leon@kernel.org
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>