Ignore and sanitize untrusted MetaAddr peer services

[teor2345]

Motivation

We have a higher level of trust in peer services that we learn directly from the peer itself.

But if we learn those services from other peers, we don't trust them very much, so we might want to:

• sanitize untrusted services
• ignore untrusted services when choosing the next peer to connect to

Specifications

The services the node advertised in its “version” message.

https://developer.bitcoin.org/reference/p2p_networking.html#addr

(The bitcoin reference and bitcoin wiki don't say much about services.)

Solution

Refactor

• make services optional (PR Make services field in MetaAddr optional #2976)
• split peer services into optional untrusted and direct fields
• update those fields correctly with each service change
• create a "services implemented by Zebra" constant

Security

• ignore untrusted services when choosing the next peer to connect to in impl Ord for MetaAddr
  • order trusted services by usefulness when selecting peers, not numeric values
    • make sure Option<PeerServices> ordering handles None and Some comparisons correctly
• consider sanitizing untrusted service fields to known bits (?)

Alternatives

This change doesn't make any difference to security until Zebra supports multiple service bits.

Even then, this change might not make much difference to security.

Related Work

The MetaAddrChange code in PRs #2273 and #2275 already has some untrusted service fields.

[ftm1000]

redistributing issues that can be separately worked from this epic #2311

[teor2345]

Zcash doesn't really use this field, so this change is not required.