The behaviours still do not match, unsurprisingly, but now we know where a
primary difference is: the Rust is validating version ranges more than the C,
so in the C it's possible to call protover_all_supported on a ridiculous
version range like "Sleen=0-4294967294" because the C uses
MAX_PROTOCOLS_TO_EXPAND to count the number of *subprotocols* whereas the Rust
uses it to count the total number of *versions* of all subprotocols.