security/strongswan: update to 5.9.8

ChangeLog: https://github.com/strongswan/strongswan/releases/tag/5.9.8

Fixes CVE-2022-40617.

PR: 267037
Reported by: franco@opnsense.org
Approved by: strongswan@Nanoteq.com (maintainer, implicit)
MFH: 2022Q4 (security update)
Security: CVE-2022-40617 DoS attack vulnerability