Clean dead paths from peers.
Increase maximum packet fragments to make room for huge multicasts with certificates of membership tagged onto them. This likely will not actually increase the number of fragments in practice much, since these are then subsequently compressed. But the buffer needs to be allocated with room for them, otherwise these packets get dropped with a range_error exception internally.
Oops... turns out we need to differentiate incoming from outgoing TCP and indeed learn incoming TCP paths. Otherwise the recipient of a TCP connection does not know to reply via TCP! Heh.