DDSSEC12 — Provide pre-shared protection for unauthenticated messages

There is an inherent DoS network amplification attack that exploits peer-to-peer discovery. See https://issues.omg.org/browse/DDSIRTP26-6

This issue should be addressed by DDS-Security. Likely using some pre-shared key mechanics to protect all messages not otherwise protected. For example, the authentication handshakes.