NFS: Allow text-based mounts via compat_sys_mount

The compat_sys_mount() system call throws EINVAL for text-based NFSv4
mounts.

The text-based mount interface assumes that any mount option blob that
doesn't set the version field to "1" is a C string (ie not a legacy
mount request).  The compat_sys_mount() call treats blobs that don't
set the version field to "1" as an error.  We just relax the check in
compat_sys_mount() a bit to allow C strings to be passed down to the NFSv4
client.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/compat.c

@@ -702,9 +702,6 @@ static int do_nfs4_super_data_conv(void *raw_data)
 		real->flags = raw->flags;
 		real->version = raw->version;
 	}
-	else {
-		return -EINVAL;
-	}
 
 	return 0;
 }