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(())
 }
 

substrate/core/cli/src/params.rs

@@ -118,6 +118,11 @@ pub struct NetworkConfigurationParams {
 	#[structopt(long = "in-peers", value_name = "IN_PEERS", default_value = "25")]
 	pub in_peers: u32,
 
+	/// By default, the network will use mDNS to discover other nodes on the local network. This
+	/// disables it.
+	#[structopt(long = "no-mdns")]
+	pub no_mdns: bool,
+
 	#[allow(missing_docs)]
 	#[structopt(flatten)]
 	pub node_key_params: NodeKeyParams