Introduce a new status "Unknown", which I'll use to annotate things
that I haven't yet checked for.
if_em is now INTR_MPSAFE. Add if_ep, which is busma-safe and INTR_MPSAFE. if_fxp is now INTR_MPSAFE. if_sis is now INTR_MPSAFE. Add if_wi, which is INTR_MPSAFE. Assign sos as ata owner due to observations of practical reality. pst is now INTR_MPSAFE. hifn is now INTR_MPSAFE. ubsec is now INTR_MPSAFE.