vere: initial stateless forwarding in ames.c
vere: initial stateless forwarding in ames.c

When receiving a packet for which we are not the recipient, attempt to
forward it statelessly. This means scrying a lane for the recipient out
of ames, then (if necessary) updating the origin lane in the packet and
sending the updates packet over the lane resulting from the scry.

Remaining work listed among the TODOs:
- implement a cap on the amount of pending to-forward packets we hold,
- handle version mismatches in the sponsee case,
- track counters around filtering & forwarding packets,
- test for memory leaks more aggressively.

ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit