pf: ensure 'off' is always set before use

If we bail out early from pf_test(6)() we still need to clean up/finish
SCTP multihome work, which requires the 'off' value to be set. Set it
early enough.

MFC after: 3 days
Sponsored by: Orange Business Services

(cherry picked from commit aefda9c92da6571d405e1b27c5c68333ad8bbc57)