This introduces interfaces to represent the packet forwarding
mechanism, and brings all the scattered UDP-related code together into
a single implementation.
This is not a pure refactoring, although much of the code in sleeve.go
has been copied from pre-existing code, and the UDP protocol remains
the same in spirit. The biggest change is the organization of the
forwarder goroutines (there is now one instead of two, and that
goroutine does a lot of auxiliary work as well as forwarding).
Performance testing between VMs on my laptop suggests that packet
throughput has not gone down, and may even have improved slightly.
David Wragg
9956d422f2
