relax ping to 10s of inactivity

llarp/link/server.cpp

@@ -297,7 +297,8 @@ namespace llarp
     auto itr   = range.first;
     while(itr != range.second)
     {
-      itr->second->SendKeepAlive();
+      if(itr->second->ShouldPing())
+        itr->second->SendKeepAlive();
       ++itr;
     }
   }

llarp/link/session.hpp

@@ -61,6 +61,9 @@ namespace llarp
 
     /// renegotiate session when we have a new RC locally
     std::function< bool(void) > RenegotiateSession;
+
+    /// return true if we should send an explicit keepalive message
+    std::function< bool(void) > ShouldPing;
   };
 }  // namespace llarp
 

llarp/link/utp.cpp

@@ -591,6 +591,11 @@ namespace llarp
 
       SendQueueBacklog = [&]() -> size_t { return sendq.size(); };
 
+      ShouldPing = [&]() -> bool {
+        auto dlt = lastActive - parent->Now();
+        return dlt >= 10000;
+      };
+
       SendKeepAlive = [&]() -> bool {
         if(state == eSessionReady)
         {