Function rf_override 

fn rf_override<T>(
    value: Option<&String>,
    what: &str,
    range: RangeInclusive<u64>,
) -> Result<Option<T>>
where
    T: TryFrom<u64>,

Parse an RF override that the dialog leaves empty when unset.

Wireshark sends the flag with an empty value for a string argument the user did not fill in, which has to mean “leave the radio alone” rather than “set it to zero”.