Avoid fault diagnosis if multiple vdevs have errors

When multiple drives are throwing errors, it is likely not
a drive failing but rather a failure above the drives, like
a controller. The active cases context of the drive's peers
is now considered when making a diagnosis.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Don Brady <don.brady@klarasystems.com>
Closes #16531