network: Only insert global addresses into the DHT. (#5735)

* network: Only insert global addresses into the DHT.

Currently every address reported via libp2p-identify is inserted into
the DHT which thus contains a multitude of unreachable addresses such
as from 127.0.0.0/8 or 10.0.0.0/8.

Issue #5099 suggested a dedicated service over UDP to gauge the
reachability of an address, which would however incur extra I/O costs
and be of limited use.

As an alternative and simpler tactic, this PR only allows global IP
addresses to be inserted into the DHT unless an explicit command-line
flag `--allow-non-global-addresses-in-dht` is given or a node is
started with `--dev`. This opt-in behaviour is meant to allow
site-local networks to still make use of a DHT.

* Enable non-global in more test setups.

* Replace command-line option with different name.

* Another test fix.

substrate/client/cli/src/params/network_params.rs

@@ -89,6 +89,12 @@ pub struct NetworkParams {
 	/// enough confidence that this feature is properly working.
 	#[structopt(long)]
 	pub no_yamux_flow_control: bool,
+
+	/// Enable peer discovery on local networks.
+	///
+	/// By default this option is true for `--dev` and false otherwise.
+	#[structopt(long)]
+	pub discover_local: bool,
 }
 
 impl NetworkParams {
@@ -141,6 +147,7 @@ impl NetworkParams {
 				use_yamux_flow_control: !self.no_yamux_flow_control,
 			},
 			max_parallel_downloads: self.max_parallel_downloads,
+			allow_non_globals_in_dht: self.discover_local || is_dev
 		}
 	}
 }