serialize: add serialize_fd_many() helper

src/basic/fd-util.h

@@ -30,6 +30,7 @@ static inline int safe_close_above_stdio(int fd) {
 }
 
 void close_many(const int fds[], size_t n_fd);
+void close_many_and_free(int *fds, size_t n_fds);
 
 int fclose_nointr(FILE *f);
 FILE* safe_fclose(FILE *f);