Creates inbound connections with other peers. Generic over the
codec applied to the framed accepted streams so the same accept
machinery serves the peer data-plane (PeerNetMsgCodec) and the
kademlia lookup-plane (KadNetMsgCodec).
Listener for byte-stream transports (TCP, TLS). Accepting is split in
two phases: accept does only the cheap kernel accept, handshake
runs the TLS upgrade. QUIC uses a separate StreamMux path.