config+server+networktest: make trickleDelay configurable

Add option to set trickleDelay for AuthenticatedGossiper in
command line, with default value of 300 milliseconds. Pass this
value to newServer, which uses it when creating a new instance of
AuthenticatedGossiper. Also set this value to 300 milliseconds when
creating nodes in integration tests.

server.go

@@ -295,7 +295,7 @@ func newServer(listenAddrs []string, chanDB *channeldb.DB, cc *chainControl,
 		Broadcast:        s.BroadcastMessage,
 		SendToPeer:       s.SendToPeer,
 		ProofMatureDelta: 0,
-		TrickleDelay:     time.Millisecond * 300,
+		TrickleDelay:     time.Millisecond * time.Duration(cfg.TrickleDelay),
 		RetransmitDelay:  time.Minute * 30,
 		DB:               chanDB,
 		AnnSigner:        s.nodeSigner,