checkpatch: discourage GSlice API

contrib/scripts/checkpatch.pl

@@ -206,6 +206,7 @@ complain ("Define setting properties with _nm_setting_property_define_direct_*()
 complain ("Use nm_g_array_{index,first,last,index_p}() instead of g_array_index(), as it nm_assert()s for valid element size and out-of-bound access") if $line =~ /\bg_array_index\b/;
 complain ("Use spaces instead of tabs") if $line =~ /\t/;
 complain ("Prefer implementing private pointers via _NM_GET_PRIVATE() or _NM_GET_PRIVATE_PTR() (the latter, if the private data has an opqaue pointer in the header file)") if $line =~ /\b(g_type_class_add_private|G_TYPE_INSTANCE_GET_PRIVATE)\b/;
+complain ("Avoid GSlice API, instead of g_malloc() or nm_slice*().") if $line =~ /\bg_slice_/;
 
 # Further on we process stuff without comments.
 $_ = $line;