security/strongswan: Update to 6.0.3

ChangeLog:
https://github.com/strongswan/strongswan/releases/tag/6.0.3

PR: 290578
Reviewed by: brd
MFH: 2025Q4
Security: CVE-2025-62291
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit c3584a2ee57c1df6b8ca6ac8b739a1245b868053)