quick-mode: Promote selected DH group instead of stripping all others

Since only the first DH group is encoded for IKEv1 this should have the
same effect as removing all other groups.

src/libcharon/sa/ikev1/tasks/quick_mode.c

@@ -802,7 +802,7 @@ static linked_list_t *get_proposals(private_quick_mode_t *this,
 				proposal->destroy(proposal);
 				continue;
 			}
-			proposal->strip_dh(proposal, group);
+			proposal->promote_dh_group(proposal, group);
 		}
 		proposal->set_spi(proposal, this->spi_i);
 	}