ipmi: do not omit lun in BMC addresses

Some systems put sensors on non-0 lun, so we should not omit it. This
was the only difference with the Linux driver, where DIMM sensors could
be queried, but not on FreeBSD.

See this report[1] on the FreeBSD forums:
https://forums.freebsd.org/threads/freebsd-cannot-get-dimm-temperature-sensor-value.85166/

Reviewed by: philip
Tested by: Andrey Lanin[1]
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D35612