s390/cio: handle unknown pgroup state

When an attempt to query or modify the grouping state of a channel path
fails due to a timeout, we cannot be sure about its state. To get back to
a defined state, disband the whole path group and try again while excluding
the offending path.

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