GitLab

This commit makes all network tests use ZeroLocalTCPAddress
as the initial peer address, and then relies on
net.ListenAddresses()

This should get rid of the tcp addr clash problems.

The separation of work in the p2p pkg is as follows:

- net implements the Swarm and connectivity
- protocol has muxer and header protocols
- host implements protocol muxing + services
- identify took over handshake completely! yay.
- p2p package works as a whole

The net package is the next to move. It will be massaged
a bit still to fix the Network / "NetworkBackend" conflict.