NFSD: don't report compiled-out versions as present

The /proc/fs/nfsd/versions file calls nfsd_vers() to check whether
the particular nfsd version is present/available. The problem is
that once I turn off e.g. NFSD-V4 this call returns -1 which is
true from the callers POV which is wrong.

The proposal is to report false in that case.

The bug has existed since 6658d3a7bbfd1768 "[PATCH] knfsd: remove
nfsd_versbits as intermediate storage for desired versions".

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: stable@kernel.org
Acked-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 171699e..06b2a26 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -120,7 +120,7 @@
 int nfsd_vers(int vers, enum vers_op change)
 {
 	if (vers < NFSD_MINVERS || vers >= NFSD_NRVERS)
-		return -1;
+		return 0;
 	switch(change) {
 	case NFSD_SET:
 		nfsd_versions[vers] = nfsd_version[vers];