ike: Optionally allow private algorithms for IKE/CHILD_SAs

Charon refuses to make use of algorithms IDs from the private space
for unknown peer implementations [1]. If you chose to ignore and violate
that section of the RFC since you *know* your peers *must* support those
private IDs, there's no way to disable that behavior.

With this commit a strongswan.conf option is introduced which allows to
deliberately ignore parts of section 3.12 from the standard.

[1] http://tools.ietf.org/html/rfc7296#section-3.12

Signed-off-by: Thomas Egerer <thomas.egerer@secunet.com>

conf/options/charon.opt

@@ -8,6 +8,10 @@ charon {}
 	**charon-cmd** instead of **charon**). For many options defaults can be
 	defined in the **libstrongswan** section.
 
+charon.accept_private_algs = no
+	Deliberately violate the IKE standard's requirement and allow the use of
+	private algorithm identifiers, even if the peer implementation is unknown.
+
 charon.accept_unencrypted_mainmode_messages = no
 	Accept unencrypted ID and HASH payloads in IKEv1 Main Mode.