[CSL-1672] Set relay networking policy
[CSL-1672] Set relay networking policy

- increase the MaxAhead for messages to 200, to match the current
  mempool size
- set the rate limiting towards core nodes to 3 Hz

These settings led to a decent throughput of ~6 transactions per
second, while keeping the core network running stably even when the
relays were exposed to higher transaction rates.

input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype,input-output-hk/pos-haskell-prototype,input-output-hk/cardano-sl,input-output-hk/pos-haskell-prototype