Add support for mDNS (#2153)

* Use libp2p 0.6.0 instead of a custom branch

* Add support for mDNS

* Fix tests

* Nit

substrate/core/cli/src/lib.rs

@@ -359,6 +359,8 @@ fn fill_network_configuration(
 	config.in_peers = cli.in_peers;
 	config.out_peers = cli.out_peers;
 
+	config.enable_mdns = !cli.no_mdns;
+
 	Ok(())
 }