EthernetServer::available() returns any socket with data, including the
already-connected client's socket. The companion path then called stop()
on what it thought was a duplicate client, closing the shared socket and
disconnecting the companion after the first packet.
Switch both SerialEthernetInterface and EthernetCLI to server.accept(),
which only returns newly-accepted sockets. Removes the IP/port duplicate
detection in the companion path (no longer reachable) and the same-socket
early-return in the CLI path.
Reported by mcode6726 on PR #1983.
Ryan Gregg
40bd7d511b