Re: [sr-dev] [kamailio/kamailio] topos: disable multiple comma separated values in One Single Via, Record-Route or Route header if needed (PR #3220)

The name of the parameter `separate_header_values` should be changed to `header_mode` to be even more generic and reused if anything else related to header management needs to be added in the future (e.g., add Via before or after Route). From implementation point of view, the current solution is "good enough" because it is doing a basic split on comma, working with the common format seen for these headers. Otherwise, at least the `Record/-Route` can have comma in its value, being defined as `name-addr` by grammar and in the eventuality of a display name, comma is allowed inside. Not sure if Via is allowed to have quoted value parameter, because I think inside it is also allowed to have comma. Anyhow, given that this commit adds this behaviour for particular deployments when some UA doesn't support headers with multiple comma separated values, I am fine to merge the implementation as it is, after renaming the parameter.