glx: Set ContextTag for all contexts

Currently, xorgGlxMakeCurrent() would set the context tag only for indirect GLX contexts.

However, several other places expect to find a context for the tag or they would raise a GLXBadContextTag error, such as WaitGL() or WaitX().

Set the context tag for direct contexts as well, to avoid raising an error and possibly killing the client.

Thanks to Erik Kurzinger ekurzinger@nvidia.com for spotting the issue.

Signed-off-by: Olivier Fourdan ofourdan@redhat.com