strongswan: gmpdh plugin, package and strongswan-isakmp metapackage

strongswan: gmpdh plugin, package and strongswan-isakmp metapackage

gmpdh plugin implements DH Groups (same as normal GMP plugin), but links to GMP statically and is stripped of all RSA based stuff. Binary size for plugin is ~20kbytes with no dependency on libgmp (200+ kbytes after squash), easilly fitting into flash space restricted devices.

strongswan-isakmp metapackage defines a minimal set of strongswan plugins (including gmpdh) for ISAKMP / IKEv1 PSK tunnels. Will fit even 4mb routers (like tplink wr841n) with disabled IPv6 support and packages (so its a trade - IPv6 or ipsec tunnels).

Signed-of-by: Mikalai Miadzvedz <[email protected]>