Log how many nodes/channels we have synced when we try to route

A common issue in LN is not having fully synced the network graph
when we attempt to send a payment. This should be improved
substantially with gossip v1.5, but for now we should improve our
debugability by logging how many nodes we have in our graph when
we attempt to find a route.

Author: TheBlueMatt

lightning/src/routing/router.rs

@@ -1989,10 +1989,11 @@ where L::Target: Logger {
 
 	let max_total_routing_fee_msat = route_params.max_total_routing_fee_msat.unwrap_or(u64::max_value());
 
-	log_trace!(logger, "Searching for a route from payer {} to {} {} MPP and {} first hops {}overriding the network graph with a fee limit of {} msat",
+	log_trace!(logger, "Searching for a route from payer {} to {} {} MPP and {} first hops {}overriding the network graph of {} nodes and {} channels with a fee limit of {} msat",
 		our_node_pubkey, LoggedPayeePubkey(payment_params.payee.node_id()),
 		if allow_mpp { "with" } else { "without" },
 		first_hops.map(|hops| hops.len()).unwrap_or(0), if first_hops.is_some() { "" } else { "not " },
+		network_graph.nodes().len(), network_graph.channels().len(),
 		max_total_routing_fee_msat);
 
 	// Step (1).