Use default testnet port on testnet when Zcash listener address is not supplied

[teor2345]

Motivation

I think there might be a bug in the deserializer code:

zebra/zebra-network/src/config.rs

Lines 312 to 324 in f1bedaf

	impl Default for DConfig {
	fn default() -> Self {
	let config = Config::default();
	Self {
	listen_addr: config.listen_addr.to_string(),
	network: config.network,
	initial_mainnet_peers: config.initial_mainnet_peers,
	initial_testnet_peers: config.initial_testnet_peers,
	peerset_initial_target_size: config.peerset_initial_target_size,
	crawl_new_peer_interval: config.crawl_new_peer_interval,
	}
	}
	}

What happens is that if the user configures Testnet but no listener address, we get the default mainnet port, as specified in the defaults here.

This usability bug only impacts testnet.

Solution

I think the default deserialized listen address needs to be "0.0.0.0", so that we get the correct default port when the address is not configured on testnet.

Originally posted by @teor2345 in #6228 (comment)

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