Failure of userland copy should return EFAULT

Many key internal functions pass system return codes that are safe to
return to userland. In the case of ddi_copyin(9F), an error passes -1
and the documentation states very clearly that drivers should pass
EFAULT to userland when this happens.

http://illumos.org/man/9F/ddi_copyin

This does not happen in the ZFS source code. I believe it should be
changed to pass EFAULT. I caught this when writing man pages for the
libzfs_core API.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3575

Author: ryao

module/zfs/zfs_ioctl.c

@@ -1334,7 +1334,7 @@ get_nvlist(uint64_t nvl, uint64_t size, int iflag, nvlist_t **nvp)
 	if ((error = ddi_copyin((void *)(uintptr_t)nvl, packed, size,
 	    iflag)) != 0) {
 		vmem_free(packed, size);
-		return (error);
+		return (SET_ERROR(EFAULT));
 	}
 
 	if ((error = nvlist_unpack(packed, size, &list, 0)) != 0) {