LU-14301 client: use EOPNOTSUPP instead of ENOTSUPP

LU-14301 client: use EOPNOTSUPP instead of ENOTSUPP

Don't return NFS-specific error code ENOTSUPP back to userspace,
instead use EOPNOTSUPP.  ENOTSUPP does not print a useful error
message from strerror() if it is hit by an application.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Iabd07b31069737e8ee7ca2382fd8cff6143ebbe5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51511
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: jsimmons <jsimmons@infradead.org>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>