s390/cio: recover from bad paths

s390/cio: recover from bad paths

In some situations we don't receive notification from firmware that
a previously unusable channelpath is usable again.

Schedule recovery for devices that return from path verification
without using all potentially usable paths. The recovery thread will
periodically trigger a path verification on the affected devices.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Suggested-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>