buildroot

strongswan: add upstream security patch

Fixes CVE-2017-11185: The gmp plugin in strongSwan before 5.6.0 allows
remote attackers to cause a denial of service (NULL pointer dereference and
daemon crash) via a crafted RSA signature.

For more details, see
https://www.strongswan.org/blog/2017/08/14/strongswan-vulnerability-%28cve-2017-11185%29.html

While we're at it, add hashes for the license files.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>