wired: fix -std=c23 build failure

gcc-15 switched to -std=c23 by default:

    https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=55e3bd376b2214e200fa76d12b67ff259b06c212

As a result `iwd` fails the build as:

    wired/ethdev.c: In function 'pae_open':
    wired/ethdev.c:340:55:
      error: passing argument 4 of 'l_io_set_read_handler'
        from incompatible pointer type [-Wincompatible-pointer-types]
      340 |         l_io_set_read_handler(pae_io, pae_read, NULL, pae_destroy);
          |                                                       ^~~~~~~~~~~
          |                                                       |
          |                                                       void (*)(void)
    In file included from ...-ell-0.70-dev/include/ell/ell.h:19,
                     from wired/ethdev.c:38:
    ...-ell-0.70-dev/include/ell/io.h:33:68:
      note: expected 'l_io_destroy_cb_t' {aka 'void (*)(void *)'}
        but argument is of type 'void (*)(void)'
       33 |                                 void *user_data, l_io_destroy_cb_t destroy);
          |                                                  ~~~~~~~~~~~~~~~~~~^~~~~~~

C23 changed the meaning of `void (*)()` from partially defined prototype
to `void (*)(void)`.

wired/ethdev.c

@@ -312,8 +312,9 @@ static bool pae_read(struct l_io *io, void *user_data)
 	return true;
 }
 
-static void pae_destroy()
+static void pae_destroy(void * user_data)
 {
+	(void)user_data;
 	pae_io = NULL;
 }