nfsd4: fix minorversion support interface

You can turn on or off support for minorversions using e.g.

	echo "-4.2" >/proc/fs/nfsd/versions

However, the current implementation is a little wonky.  For example, the
above will turn off 4.2 support, but it will also turn *on* 4.1 support.

This didn't matter as long as we only had 2 minorversions, which was
true till very recently.

And do a little cleanup here.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4proc.c

@@ -1293,7 +1293,7 @@ nfsd4_proc_compound(struct svc_rqst *rqstp,
 	 * According to RFC3010, this takes precedence over all other errors.
 	 */
 	status = nfserr_minor_vers_mismatch;
-	if (args->minorversion > nfsd_supported_minorversion)
+	if (nfsd_minorversion(args->minorversion, NFSD_TEST) <= 0)
 		goto out;
 
 	status = nfs41_check_op_ordering(args);