IO stall after deleting and path checker changes after reenabling zfcp device

Setting one zfcp device offline using chccwdev in a multipath
environment and waiting will lead to IO stall on all paths.
After setting the zfcp device back online using chccwdev,
the devices with io stall will have a different path checker.
Devices corresponding to the deleted units are never freed.
This has the effect that 'slave_destroy' is never called and zfcp
still thinks that this unit is registered
(ZFCP_STATUS_UNIT_REGISTERED is still set). Hence the erp
routine is not called correctly and the unit is not enabled properly.

Do not delete rport and the sdev. Just set the host to block on
'offline'. Setting host online again will then remove the blocked status
and everything is fine again.
Signed-off-by: NMichael Loehr <mloehr2@linux.vnet.ibm.com>
Signed-off-by: NSwen Schillig <swen@vnet.ibm.com>
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>