swarm/network: DRY out repeated giga comment

I not necessarily agree with the way we wait for event propagation.
But I truly disagree with having duplicated giga comments.

swarm/network/simulation/node_test.go

@@ -339,16 +339,7 @@ func TestStartStopNode(t *testing.T) {
 		t.Error("node not stopped")
 	}
 
-	// Sleep here to ensure that Network.watchPeerEvents defer function
-	// has set the `node.Up = false` before we start the node again.
-	// p2p/simulations/network.go:215
-	//
-	// The same node is stopped and started again, and upon start
-	// watchPeerEvents is started in a goroutine. If the node is stopped
-	// and then very quickly started, that goroutine may be scheduled later
-	// then start and force `node.Up = false` in its defer function.
-	// This will make this test unreliable.
-	time.Sleep(time.Second)
+	waitForPeerEventPropagation()
 
 	err = sim.StartNode(id)
 	if err != nil {
@@ -386,16 +377,7 @@ func TestStartStopRandomNode(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	// Sleep here to ensure that Network.watchPeerEvents defer function
-	// has set the `node.Up = false` before we start the node again.
-	// p2p/simulations/network.go:215
-	//
-	// The same node is stopped and started again, and upon start
-	// watchPeerEvents is started in a goroutine. If the node is stopped
-	// and then very quickly started, that goroutine may be scheduled later
-	// then start and force `node.Up = false` in its defer function.
-	// This will make this test unreliable.
-	time.Sleep(time.Second)
+	waitForPeerEventPropagation()
 
 	idStarted, err := sim.StartRandomNode()
 	if err != nil {
@@ -431,16 +413,7 @@ func TestStartStopRandomNodes(t *testing.T) {
 		}
 	}
 
-	// Sleep here to ensure that Network.watchPeerEvents defer function
-	// has set the `node.Up = false` before we start the node again.
-	// p2p/simulations/network.go:215
-	//
-	// The same node is stopped and started again, and upon start
-	// watchPeerEvents is started in a goroutine. If the node is stopped
-	// and then very quickly started, that goroutine may be scheduled later
-	// then start and force `node.Up = false` in its defer function.
-	// This will make this test unreliable.
-	time.Sleep(time.Second)
+	waitForPeerEventPropagation()
 
 	ids, err = sim.StartRandomNodes(2)
 	if err != nil {
@@ -457,3 +430,15 @@ func TestStartStopRandomNodes(t *testing.T) {
 		}
 	}
 }
+
+func waitForPeerEventPropagation() {
+	// Sleep here to ensure that Network.watchPeerEvents defer function
+	// has set the `node.Up() = false` before we start the node again.
+	//
+	// The same node is stopped and started again, and upon start
+	// watchPeerEvents is started in a goroutine. If the node is stopped
+	// and then very quickly started, that goroutine may be scheduled later
+	// then start and force `node.Up() = false` in its defer function.
+	// This will make this test unreliable.
+	time.Sleep(1 * time.Second)
+}