>	aha, put a mark on routing table for foo/32... not sure.  i guess
>	defininng RTF_xx for this is too much.

	marking a route with RTV_MTU flag seems too much for me, as the way we
	detect the PMTUD blackhole is very unreliable (there's no way to
	reliably detect PMTUD breakage, i guess).

itojun