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.

libnm-core/nm-keyfile-utils.c

@@ -106,7 +106,7 @@ nm_keyfile_plugin_kf_set_##stype##_list (GKeyFile *kf, \
 	const char *alias; \
  \
 	alias = nm_keyfile_plugin_get_alias_for_setting_name (group); \
-	g_key_file_set_##stype##_list (kf, alias ? alias : group, key, list, length); \
+	g_key_file_set_##stype##_list (kf, alias ?: group, key, list, length); \
 }
 
 DEFINE_KF_LIST_WRAPPER(integer, gint*, gint);
@@ -170,7 +170,7 @@ nm_keyfile_plugin_kf_set_##stype (GKeyFile *kf, \
 	const char *alias; \
  \
 	alias = nm_keyfile_plugin_get_alias_for_setting_name (group); \
-	g_key_file_set_##stype (kf, alias ? alias : group, key, value); \
+	g_key_file_set_##stype (kf, alias ?: group, key, value); \
 }
 
 DEFINE_KF_WRAPPER(string, gchar*, const gchar*);