nfs: report the inode version in getattr if requested

Allow NFS to report the i_version in getattr requests. Since the cost to
fetch it is relatively cheap, do it unconditionally and just set the
flag if it looks like it's valid. Also, conditionally enable the
MONOTONIC flag when the server reports its change attr type as such.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>