Only use filterInventoryKnown with MSG_TX inventory messages.

Previously this logic could erroneously filter a MSG_BLOCK inventory message.

src/net.h

@@ -501,7 +501,8 @@ public:
     {
         {
             LOCK(cs_inventory);
-            if (!filterInventoryKnown.contains(inv.hash))
+            if (inv.type == MSG_TX && filterInventoryKnown.contains(inv.hash))
+                return;
             vInventoryToSend.push_back(inv);
         }
     }