TCP: handle concurrent connections more gracefully

When A connects to B and B connects to A concurrently, and no existing connections are present, then one member (with the higher address) will prevail, and the other one will close its connection and drop the message.

This is not usually an issue, as higher-up layers will retransmit the message, thus re-establishing the connection.
However, if we have a protocol based on negative acks, such as UNICAST2, the retransmission might take a while if that message was the last one.

SOLUTION:
The end that closes the connection should simply resend the message once, thus re-creating the connection.