pf: fix overly large copy in pf_rule_to_krule()

The timeout array in struct pf_rule has PFTM_OLD_MAX entries, the one in
struct pf_krule has PFTM_MAX entries (and PFTM_MAX > PFTM_OLD_MAX).
Use the smaller of the sizes when copying.

Reported by: CheriBSD
MFC after: 1 week
Event: Kitchener-Waterloo Hackathon 202406