icmp: when logging ICMP ratelimiting message use correct jitter value

The limiting of the very last second has been done using certain jitter
value. We update the jitter for the next second. But the logging should
report the jitter before the change.

Reviewed by: kp, tuexen, zlei
Differential Revision: https://reviews.freebsd.org/D44477
Approved by: re (cperciva)

(cherry picked from commit b508545ce044dbfdd83da772e73f969a3713d59d)
(cherry picked from commit a71eee300ba7d94a1621c7b31eaaa79243db84ec)