plugin-feature: Add vendor specific EAP method registration macros

Vendor specific EAP methods may be registered with:

    PLUGIN_CALLBACK(eap_method_register, <constructor>),
        PLUGIN_PROVIDE(EAP_SERVER_VENDOR, <type>, <vendor>),

Same for client implementations via EAP_PEER_VENDOR.

References #969.

src/libcharon/sa/eap/eap_method.c

@@ -30,7 +30,8 @@ bool eap_method_register(plugin_t *plugin, plugin_feature_t *feature,
 {
 	if (reg)
 	{
-		charon->eap->add_method(charon->eap, feature->arg.eap, 0,
+		charon->eap->add_method(charon->eap, feature->arg.eap.type,
+					feature->arg.eap.vendor,
 					feature->type == FEATURE_EAP_SERVER ? EAP_SERVER : EAP_PEER,
 					(eap_constructor_t)data);
 	}