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 <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>

fs/compat.c

···
 		real->flags = raw->flags;
 		real->version = raw->version;
 	}
-	else {
-		return -EINVAL;
-	}
 
 	return 0;
 }