security/ipsec-tools: fix build for FreeBSD 15

FreeBSD 15.0 got some incompatible changes to the header
/usr/include/netipsec/ipsec.h breaking build of this legacy code
due to added "const".

Fix it providing some patches that do not change the behavior.
While here, suppress some warnings that pollute build log
using modern Clang.

This fixes build, so PORTREVISION not bumped.