kdc: add audit plugin API to windc API

Allow the windc plugin to also implement an audit callback. As part of this
change, both the HDB and windc audit function signatures are changed to return
void.

kdc/krb5tgs.c

@@ -2578,7 +2578,7 @@ _kdc_tgs_rep(astgs_request_t r)
 
 out:
     r->ret = ret;
-    _kdc_hdb_audit(r);
+    _kdc_audit_request(r);
 
     if(ret && ret != HDB_ERR_NOT_FOUND_HERE && data->data == NULL){
 	METHOD_DATA error_method = { 0, NULL };