Increase duration of message cache from two blocks (which in practice meant anything > 1 block) to 30 blocks, and move the constant to config.hpp

libraries/net/include/graphene/net/config.hpp

@@ -51,6 +51,14 @@
 
 #define GRAPHENE_NET_MAXIMUM_QUEUED_MESSAGES_IN_BYTES        (1024 * 1024)
 
+/**
+ * When we receive a message from the network, we advertise it to
+ * our peers and save a copy in a cache were we will find it if
+ * a peer requests it.  We expire out old items out of the cache
+ * after this number of blocks go by.
+ */
+#define GRAPHENE_NET_MESSAGE_CACHE_DURATION_IN_BLOCKS        30
+
 /**
  * We prevent a peer from offering us a list of blocks which, if we fetched them
  * all, would result in a blockchain that extended into the future.

libraries/net/node.cpp

@@ -120,7 +120,7 @@ namespace graphene { namespace net {
     class blockchain_tied_message_cache
     {
     private:
-      static const uint32_t cache_duration_in_blocks = 2;
+      static const uint32_t cache_duration_in_blocks = GRAPHENE_NET_MESSAGE_CACHE_DURATION_IN_BLOCKS;
 
       struct message_hash_index{};
       struct message_contents_hash_index{};