This should meet the following requirements: - only one probe in flight, - not too often (500ms delay min), - increase SRTT on idle flows.
- with remote addresses learn by get_addr_info, - with remote addresses learn by the server. Don't remove old flows. This idea may be bad: we should probably remove flows when we lost our local address, however this may be possibly done on error, when sending.
The server will have the same flow ID than the client, for each flow. This way, if the client use an explicit flow (src, dst) with a "system" flow (_, dst), and if the kernel decide to use "src" as the source, then the two flows will now be consider different by the client.