dcrd: Do not send a wakeup if not sleeping (#314)

A simple printf shows dozens of AfterFuncs being generated, especially
on testnet where the connectable node count is currently low.  By
resetting the timer, it prevents needless wakeups from filling the
channel.

server.go

@@ -1827,7 +1827,8 @@ func (s *server) peerHandler() {
 	}
 
 	// if nothing else happens, wake us up soon.
-	time.AfterFunc(10*time.Second, func() { s.wakeup <- struct{}{} })
+	wakeupAfter := 10 * time.Second
+	timer := time.AfterFunc(wakeupAfter, func() { s.wakeup <- struct{}{} })
 
 out:
 	for {
@@ -1946,9 +1947,7 @@ out:
 
 		// We need more peers, wake up in ten seconds and try again.
 		if state.NeedMoreOutbound() {
-			time.AfterFunc(10*time.Second, func() {
-				s.wakeup <- struct{}{}
-			})
+			timer.Reset(wakeupAfter)
 		}
 	}