If we can guarantee the lifetime of the fd is longer than
the memory, we can use DONT_CLOSE flag not to close when release.
But it's not provided in gstdmabuf yet while gstfdmemory does.

For example, in case of using VA-API or MSDK, we would need this api.
Otherwise we should call dup to duplicate the fd.

https://bugzilla.gnome.org/show_bug.cgi?id=794829