Potential P2P Bandwidth attack

[yeastplume]

Logging and taking note of a potential attack reported to dogecoin that could result in an attacker causing a node to use excessive bandwidth:

dogecoin/dogecoin#3243

While this attack can be more generalized to P2P systems as opposed to anything Grin-specific, it's still something we'll want to mitigate, particularly for PIBD requests. We'll continue to monitor the original issue and consider what mitigations might be feasible.