all: use the elvis operator wherever possible

Coccinelle:

  @@
  expression a, b;
  @@
  -a ? a : b
  +a ?: b

Applied with:

  spatch --sp-file ternary.cocci --in-place --smpl-spacing --dir .

With some manual adjustments on spots that Cocci didn't catch for
reasons unknown.

Thanks to the marvelous effort of the GNU compiler developer we can now
spare a couple of bits that could be used for more important things,
like this commit message. Standards commitees yet have to catch up.

examples/C/glib/get-ap-info-libnm.c

@@ -180,7 +180,7 @@ show_wifi_device_info (NMDevice *device)
 	speed /= 1000;
 
 	printf ("Device: %s  ----  Driver: %s  ----  Speed: %d Mbit/s  ----  Active AP: %s\n",
-	         iface, driver, speed, active_ssid_str ? active_ssid_str : "none");
+	         iface, driver, speed, active_ssid_str ?: "none");
 	printf ("=================================================================================\n");
 	g_free (active_ssid_str);