p2p: Increase tx relay rate

In the presence of smaller transactions on the network, blocks can sustain a
higher relay rate than 7tx/second. In this event, the per-peer inventory queues
can grow too large.

This commit bumps the rate up to 14 tx/s (for inbound peers), increasing the
safety margin by a factor of 2.

Outbound peers continue to receive relayed transactions at 2.5x the rate of
inbound peers, for a rate of 35tx/second.

Co-Authored-By: Suhas Daftuar <[email protected]>

src/net_processing.cpp

@@ -136,7 +136,7 @@ static constexpr auto INBOUND_INVENTORY_BROADCAST_INTERVAL{5s};
 static constexpr auto OUTBOUND_INVENTORY_BROADCAST_INTERVAL{2s};
 /** Maximum rate of inventory items to send per second.
  *  Limits the impact of low-fee transaction floods. */
-static constexpr unsigned int INVENTORY_BROADCAST_PER_SECOND = 7;
+static constexpr unsigned int INVENTORY_BROADCAST_PER_SECOND{14};
 /** Target number of tx inventory items to send per transmission. */
 static constexpr unsigned int INVENTORY_BROADCAST_TARGET = INVENTORY_BROADCAST_PER_SECOND * count_seconds(INBOUND_INVENTORY_BROADCAST_INTERVAL);
 /** Maximum number of inventory items to send per transmission. */