nfsd: map the ENOKEY to nfserr_perm for avoiding warning

nfsd: map the ENOKEY to nfserr_perm for avoiding warning

Now that Ext4 and f2fs filesystems support encrypted directories and
files, attempts to access those files may return ENOKEY, resulting in
the following WARNING.

Map ENOKEY to nfserr_perm instead of nfserr_io.

[ 1295.411759] ------------[ cut here ]------------
[ 1295.411787] WARNING: CPU: 0 PID: 12786 at fs/nfsd/nfsproc.c:796 nfserrno+0x74/0x80 [nfsd]
[ 1295.411806] nfsd: non-standard errno: -126
[ 1295.411816] Modules linked in: nfsd nfs_acl auth_rpcgss nfsv4 nfs lockd fscache tun bridge stp llc fuse ip_set nfnetlink vmw_vsock_vmci_transport vsock snd_seq_midi snd_seq_midi_event coretemp crct10dif_pclmul crc32_generic crc32_pclmul snd_ens1371 gameport ghash_clmulni_intel snd_ac97_codec f2fs intel_rapl_perf ac97_bus snd_seq ppdev snd_pcm snd_rawmidi snd_timer vmw_balloon snd_seq_device snd joydev soundcore parport_pc parport nfit acpi_cpufreq tpm_tis vmw_vmci tpm_tis_core tpm shpchp i2c_piix4 grace sunrpc xfs libcrc32c vmwgfx drm_kms_helper ttm drm crc32c_intel e1000 mptspi scsi_transport_spi serio_raw mptscsih mptbase ata_generic pata_acpi fjes [last unloaded: nfs_acl]
[ 1295.412522] CPU: 0 PID: 12786 Comm: nfsd Tainted: G        W       4.11.0-rc1+ #521
[ 1295.412959] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
[ 1295.413814] Call Trace:
[ 1295.414252]  dump_stack+0x63/0x86
[ 1295.414666]  __warn+0xcb/0xf0
[ 1295.415087]  warn_slowpath_fmt+0x5f/0x80
[ 1295.415502]  ? put_filp+0x42/0x50
[ 1295.415927]  nfserrno+0x74/0x80 [nfsd]
[ 1295.416339]  nfsd_open+0xd7/0x180 [nfsd]
[ 1295.416746]  nfs4_get_vfs_file+0x367/0x3c0 [nfsd]
[ 1295.417182]  ? security_inode_permission+0x41/0x60
[ 1295.417591]  nfsd4_process_open2+0x9b2/0x1200 [nfsd]
[ 1295.418007]  nfsd4_open+0x481/0x790 [nfsd]
[ 1295.418409]  nfsd4_proc_compound+0x395/0x680 [nfsd]
[ 1295.418812]  nfsd_dispatch+0xb8/0x1f0 [nfsd]
[ 1295.419233]  svc_process_common+0x4d9/0x830 [sunrpc]
[ 1295.419631]  svc_process+0xfe/0x1b0 [sunrpc]
[ 1295.420033]  nfsd+0xe9/0x150 [nfsd]
[ 1295.420420]  kthread+0x101/0x140
[ 1295.420802]  ? nfsd_destroy+0x60/0x60 [nfsd]
[ 1295.421199]  ? kthread_park+0x90/0x90
[ 1295.421598]  ret_from_fork+0x2c/0x40
[ 1295.421996] ---[ end trace 0d5a969cd7852e1f ]---

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>