xauth: add a configuration string option to be passed to XAuth instances

The configuration string is appended to the XAuth backend name, separated by
a colon. The configuration string is passed untouched to the backend, where
it can change the behavior of the XAuth module.

src/libcharon/plugins/xauth_eap/xauth_eap.c

@@ -266,7 +266,7 @@ METHOD(xauth_method_t, destroy, void,
  * Described in header.
  */
 xauth_eap_t *xauth_eap_create_server(identification_t *server,
-									 identification_t *peer)
+									 identification_t *peer, char *profile)
 {
 	private_xauth_eap_t *this;