Add support for decryption faults in zinject

This patch adds the ability for zinject to trigger decryption
and authentication faults in the ZIO and ARC layers. This
functionality is exposed via the new "decrypt" error type, which
may be provided for "data" object types.

This patch also refactors some of the core encryption / decryption
functions so that they have consistent prototypes, handle errors
consistently, and do not have unused arguments.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7474

man/man8/zinject.8

@@ -108,13 +108,14 @@ A vdev specified by path or GUID.
 .BI "\-e" " device_error"
 Specify
 .BR "checksum" " for an ECKSUM error,"
+.BR "decrypt" " for a data decryption error,"
 .BR "corrupt" " to flip a bit in the data after a read,"
 .BR "dtl" " for an ECHILD error,"
 .BR "io" " for an EIO error where reopening the device will succeed, or"
 .BR "nxio" " for an ENXIO error where reopening the device will fail."
 For EIO and ENXIO, the "failed" reads or writes still occur.  The probe simply
 sets the error value reported by the I/O pipeline so it appears the read or
-write failed.
+write failed.  Decryption errors only currently work with file data.
 .TP
 .BI "\-f" " frequency"
 Only inject errors a fraction of the time. Expressed as a real number