[Swan-dev] WIP: supporting xfrm SA expire

[Antony Antony]

Hi Paul,
Here is my sa expire branch rebased to main.

#sa-expire
https://github.com/antonyantony/libreswan/tree/sa-expire

It need a bit more work to merge to main. I look the code again and fix 
"FIXME". It also need more tests.

If you feel like helping add more tests. This would help to get the
branch ready to merge sooner than later.

regards,
-antony