nvme_rdma - leaves provider resources allocated

Assume an nvme_rdma host has one attached controller in RECONNECTING state, and
that controller has failed to reconnect at least once and thus is in the
delay_schedule time before retrying the connection.  At that moment, there are
no cm_ids allocated for that controller because the admin queue and the io
queues have been freed.  So nvme_rdma cannot get a DEVICE_REMOVAL from the
rdma_cm.  This means if the underlying provider module is removed, it will be
removed with resources still allocated by nvme_rdma.  For iw_cxgb4, this causes
a BUG_ON() in gen_pool_destroy() because MRs are still allocated for the
controller.

Thoughts on how to fix this?

Hey Steve,

I think it's time to go back to your client register proposal.

I can't think of any way to get it right at the moment...

Maybe if we can make it only do something meaningful in remove_one()
to handle device removal we can get away with it...