Ensure that `nut-ipmipsu` driver is IPv6 (and remote at all) capable

[jimklimov]

Also revised how our other drivers for networked port values parse their device_path - if anyone needs similar fixes?

• nut-ipmipsu.c currently only uses local device access, it seems; there are comments regarding syntax for remote IPMI (id?@host), but it is not parsed that way.
  • In nut-scanner there is ipmi_ctx_open_outofband scanning however. I did not quite find docs, but in sources https://fossies.org/linux/freeipmi/libfreeipmi/api/ipmi-api.c it seems the internal _setup_hostname() used in different ctx open methods does parse the "hostname" string into hostname_ptr and port_ptr.

Originally posted by @jimklimov in https://github.com/networkupstools/nut/issues/3122#issuecomment-3397392274