nfsd: don't create nfsv4recoverydir in nfsdfs when not used.

nfsd: don't create nfsv4recoverydir in nfsdfs when not used.

When CONFIG_NFSD_LEGACY_CLIENT_TRACKING is not set, the virtual file
  /proc/fs/nfsd/nfsv4recoverydir
is created but responds EINVAL to any access.
This is not useful, is somewhat surprising, and it causes ltp to
complain.

The only known user of this file is in nfs-utils, which handles
non-existence and read-failure equally well.  So there is nothing to
gain from leaving the file present but inaccessible.

So this patch removes the file when its content is not available - i.e.
when that config option is not selected.

Also remove the #ifdef which hides some of the enum values when
CONFIG_NFSD_V$ not selection.  simple_fill_super() quietly ignores array
entries that are not present, so having slots in the array that don't
get used is perfectly acceptable.  So there is no value in this #ifdef.

Reported-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Fixes: 74fd48739d04 ("nfsd: new Kconfig option for legacy client tracking")
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>