add failed connection attempt logging

src/lib/agent/PeerServer.mjs

@@ -140,7 +140,11 @@ class PeerServer extends EventEmitter {
 			new_peer => p_retry(async () => await this.add_peer(
 				new_peer.address,
 				new_peer.port
-			), { retries: this.retries })
+			), {
+				retries: this.retries,
+				onFailedAttempt: (error, attempt, left) =>
+					l.error(`[attempt ${attempt} / ${left}] Error while connecting to ${new_peer.address}:${new_peer.port}: ${error}`)
+			})
 		))).filter(peer => peer instanceof Peer);
 	}