core: swap order of "n_storage_fds" and "n_socket_fds" parameters

core: swap order of "n_storage_fds" and "n_socket_fds" parameters

When process fd lists to pass to activated programs we always place the
socket activation fds first, and the storage fds last. Irritatingly in
almost all calls the "n_storage_fds" parameter (i.e. the number of
storage fds to pass) came first so far, and the "n_socket_fds" parameter
second. Let's clean this up, and specify the number of fds in the order
the fds themselves are passed.

(Also, let's fix one more case where "unsigned" was used to size an
array, while we should use "size_t" instead.)