Nested structs makes it impossible to extend the nested struct after
extending the base struct. The union acts as a single struct in this
case but the nesting is still an issue. Use pointers to those structs instead
to keep all of them extensible. Only the struct which is applicable for the
signal type is not a null pointer to make sure only valid data is accessed.
Signed-off-by: Sebastian Wick <sebastian.wick@redhat.com>
