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/service/test/src/lib.rs

@@ -150,6 +150,8 @@ fn node_config<G: RuntimeGenesis + 'static, E: ChainSpecExtension + Clone + 'sta
 		None,
 	);
 
+	network_config.allow_non_globals_in_dht = true;
+
 	network_config.listen_addresses.push(
 		iter::once(multiaddr::Protocol::Ip4(Ipv4Addr::new(127, 0, 0, 1)))
 			.chain(iter::once(multiaddr::Protocol::Tcp(base_port + index as u16)))