syncache: Only explicitly delete unreferenced protocol-cloned routes
netstat.1: Mention routes' MSL and initial window size
route: Only delete dynamic routes on the current CPU if they are losing

Going through all CPUs for losing dynamic routes is time consuming and
does not worth the trouble.
route6: Only delete dynamic routes on the current CPU if they are losing
route: Factor out rt_domsg_global()
route: Prioritize routing messages during iface detach
route: Prioritize routing messages during iface down
route: Prioritize rtchange messages