HIM: Check if MAX_PKT_LEN > 32 works

The code in HIM seems to not support packets of more than 32 flits, with the number chosen arbitrarily?

https://github.com/opensocdebug/osd-hw/blob/osd-next/modules/him/common/osd_him.sv#L36

Double-check and possibly make this depend on MAX_PKT_LEN.