glx: Fix the swap event filter for DRI3 drivers

The drawable field is set to the X drawable ID when the swap event is
synthesized by DRI2WireToEvent(), and the GLX drawable ID when the
event is received over the wire. The latter being the case with DRI3.

__glXWireToEvent() fixes this for Xlib clients by changing the field
to the X drawable ID. This doesn't work for xcb clients however,
so we have to expect the field to be set to either the X or the GLX
drawable ID.

BUG: 342582