The ja3 package uses next instead of return and triggers the new
errors with Zeek 5.2. That seems somewhat bad.
In case we want to do a 5.2.1 that makes this a warning, this
would be change to do so.
Seemed easiest to do it via the traversal infrastructure as we do not
otherwise track enough context/scope when instantiating break or next
statements.
Might be worth moving this out of src/parse.y, but didn't exactly know
where. Or maybe we wait until there's more such trivial validations
popping up
Fixes#2440
