snapshot: support ip address literals, more docs

[rcgoodfellow]

• Add more documentation on how to use the snapshot command.
• Add support for specifying literal IP addresses as triggers since doing this in a hex/mask was very tedious.

[cfzimmerman]

Gut reaction is to ask for an expectorate test for every swadm change, but this one would be pretty tricky to test in CI, right? No pressure if so. Overall looks great.

[cfzimmerman]

Might be more readable to un-nest the matches.

    fn from(value: Trigger) -> Self {
        let (val, mask) = match value.value {
            TriggerValue::Ip { ip: IpAddr::V4(v4) } => (
                format!("0x{:08x}", u32::from(v4)),
                format!("0x{:x}", u32::MAX),
            ),
            TriggerValue::Ip { ip: IpAddr::V6(v6) } => (
                format!("0x{:032x}", u128::from(v6)),
                format!("0x{:x}", u128::MAX),
            ),
            TriggerValue::Hex { value, mask } => (value, mask),
        };
        types::SnapshotTrigger { field: value.field, mask, value: val }
    }

[cfzimmerman]

Worth a unit test?

[cfzimmerman]

Should we say "multiple unique triggers" or even enforce uniqueness? For example, I think

-t hdr.ethernet.dst_addr=A -t hdr.ethernet.dst_addr=B

only captures "B". Does that sound right to you? Might be confusing if left unstated. This is based on reading tofino sde code, so its very possible I'm incorrect.

https://github.com/oxidecomputer/tofino-sde/blob/9671e58c051b342d2031a005226caf00d951dcc5/pkgsrc/bf-drivers/src/pipe_mgr/pipe_mgr_mau_snapshot.c#L4186-L4196