HTTPS-RR `no-default-alpn` must be empty

[Gunni]

Describe the bug
For "no-default-alpn", the presentation and wire-format values be empty.

To Reproduce
Steps to reproduce the behavior:

1. Create a HTTPS("asd", 1, ".", "no-default-alpn alpn=h3,h2")
2. Look at result on provider
3. Observe no-default-alpn=""

Expected behavior
no-default-alpn is a flag, not a key/value thing?

DNS Provider
Cloudflare

Additional context
"values be empty" might mean ="" is ok, it's an empty string value?

[tlimoncelli]

Any thoughts, @fritterhoff @tresni ?

[fritterhoff]

Uff. Jep. We have to accept missing values

[fritterhoff]

Prop. we have to fix this:

dnscontrol/models/t_svcb.go

Lines 17 to 19 in 70c1feb

	for _, kv := range params {
	paramsStr = append(paramsStr, fmt.Sprintf("%s=%s", kv.Key(), kv.String()))
	}

[Gunni]

Also, the field order is irrelevant, don't modify if server has different order of fields?

Or, always use this order as if on wire?

[fritterhoff]

From my point of view we don't touch the order right now?