Replace trickle nodes with per-node/message Poisson delays

We used to have a trickle node, a node which was chosen in each iteration of
the send loop that was privileged and allowed to send out queued up non-time
critical messages. Since the removal of the fixed sleeps in the network code,
this resulted in fast and attackable treatment of such broadcasts.

This pull request changes the 3 remaining trickle use cases by random delays:
* Local address broadcast (while also removing the the wiping of the seen filter)
* Address relay
* Inv relay (for transactions; blocks are always relayed immediately)

The code is based on older commits by Patrick Strateman.

Github-Pull: #7125
Rebased-From: 5400ef6bcb

src/main.h

@@ -87,6 +87,14 @@ static const unsigned int DATABASE_WRITE_INTERVAL = 60 * 60;
 static const unsigned int DATABASE_FLUSH_INTERVAL = 24 * 60 * 60;
 /** Maximum length of reject messages. */
 static const unsigned int MAX_REJECT_MESSAGE_LENGTH = 111;
+/** Average delay between local address broadcasts in seconds. */
+static const unsigned int AVG_LOCAL_ADDRESS_BROADCAST_INTERVAL = 24 * 24 * 60;
+/** Average delay between peer address broadcasts in seconds. */
+static const unsigned int AVG_ADDRESS_BROADCAST_INTERVAL = 30;
+/** Average delay between trickled inventory broadcasts in seconds.
+ *  Blocks, whitelisted receivers, and a random 25% of transactions bypass this. */
+static const unsigned int AVG_INVENTORY_BROADCAST_INTERVAL = 5;
+
 static const unsigned int DEFAULT_LIMITFREERELAY = 15;
 static const bool DEFAULT_RELAYPRIORITY = true;
 
@@ -197,9 +205,8 @@ bool ProcessMessages(CNode* pfrom);
  * Send queued protocol messages to be sent to a give node.
  *
  * @param[in]   pto             The node which we are sending messages to.
- * @param[in]   fSendTrickle    When true send the trickled data, otherwise trickle the data until true.
  */
-bool SendMessages(CNode* pto, bool fSendTrickle);
+bool SendMessages(CNode* pto);
 /** Run an instance of the script checking thread */
 void ThreadScriptCheck();
 /** Try to detect Partition (network isolation) attacks against us */