peer: Offset ping interval from idle timeout.

This modifies the ping interval to be defined in terms of the default
idle timeout such that it is shorter and relatively prime to it to help
prevent undesirable disconnects in higher latency scenarios.

peer/peer.go

@@ -40,10 +40,6 @@ const (
 	// inventory cache.
 	maxKnownInventory = 1000
 
-	// pingInterval is the interval of time to wait in between sending ping
-	// messages.
-	pingInterval = 2 * time.Minute
-
 	// negotiateTimeout is the duration of inactivity before we timeout a
 	// peer that hasn't completed the initial version negotiation.
 	negotiateTimeout = 30 * time.Second
@@ -66,6 +62,10 @@ const (
 	// timed out when a peer is created with the idle timeout configuration
 	// option set to 0.
 	defaultIdleTimeout = 120 * time.Second
+
+	// pingInterval is the interval of time to wait in between sending ping
+	// messages.
+	pingInterval = defaultIdleTimeout - 13*time.Second
 )
 
 var (