[strongSwan] bare minimum required kernel modules/version

[Martin Willi]

>   - Will Strongswan compile on any kernel as far back as 2.6.16 too?

Yes. We require some headers in a recent version (such as linux/xfrm.h),
but we ship up-to-date headers with strongSwan (under src/include).

>   - Is it a good idea (feature/security wise) to use 2.6.16 w/ Strongswan or
>     should a user be advised to use at least kernel 2.6.xx?

Yes, unless you'll use the mentioned IPv4/v6 only kernel or want proper
SHA2 support in ESP.

Regards
Martin