Map ECKSUM and EFRAGS from ZFS onto real errnos.

Make it less confusing when, for example, stat sets errno to 122 because a
checksum failed in ZFS:

Before: getfacl: /foo/bar: stat() failed: Unknown error: 122
After: getfacl: /foo/bar: stat() failed: Integrity check failed

Submitted by:	Ryan Moeller <ryan@ixsystems.com>
Reviewed by:	mckusick, mav
MFC after:	2 weeks
Sponsored by:	iXsystems, Inc.
Differential Revision:	https://reviews.freebsd.org/D22973

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/zio.h

@@ -233,12 +233,11 @@ enum zio_wait_type {
 };
 
 /*
- * We'll take the number 122 and 123 to indicate checksum errors and
- * fragmentation. Those doesn't collide with any errno values as they
- * are greater than ELAST.
+ * These are bespoke errnos used in ZFS. We map them to their closest FreeBSD
+ * equivalents. This gives us more useful error messages from strerror(3).
  */
-#define	ECKSUM	122
-#define	EFRAGS	123
+#define	ECKSUM	EINTEGRITY
+#define	EFRAGS	ENOSPC
 
 typedef void zio_done_func_t(zio_t *zio);