Move MetaAddr serialization into zebra_network::protocol::external

[teor2345]

Motivation

To prepare for addrv2 serialization, we need to deserialize two different formats into the MetaAddr data structure.

Zebra expects each data structure to have a single format. So it doesn't provide a format argument to its deserialization functions. So I want to create two different types for deserialization: AddrV1 and AddrV2.

Solution

This is the first part of that change, which moves the MetaAddr serialization code to the zebra_network::protocol::external module.

I split the code movement from the type changes, to make them both easier to review.

Review

@jvff can review this change.

It's not urgent, but there will be a series of PRs, so it would be great to get it done by Monday.

Reviewer Checklist

• It's just code movement
• Existing tests pass

Follow Up Work

• ZIP-155: Parse addrv2 in Zebra #2681

[jvff]

Looks good! I saw one opportunity for improvement, but it's not directly part of the PR as the PR is just moving the code, so feel free to ignore it

[jvff]

Optional suggestion:

Suggested change

	let mut smallest_disallowed_vec = Vec::with_capacity(max_allocation + 1);
	for _ in 0..(MetaAddr::max_allocation() + 1) {
	smallest_disallowed_vec.push(addr);
	}
	let mut smallest_disallowed_vec = vec![addr; max_allocation + 1];

[teor2345]

I think I'll fix this on top of PR #3022, because it can be fixed in all the preallocate tests.
(And I need to write new preallocate tests in #3022.)