do what the RFC says in regards of seq_no
update all depending nodes when a shorter route is found
use non-blocking sockets
use refcounting even for local_addr
call netaddr_use on successfully found netaddr
set next_addr to addr for 1-hop neighbors
It's not really required at this point, but keep it consistent for later code that might just rely on next_addr without checking the hopcount
don't call an equally long route 'shorter', instead prefer the existing route when there is a new alternative