egl/wayland: Send commit after flushing the driver context

egl/wayland: Send commit after flushing the driver context

This typically won't make a difference, since we only send the requests at
wl_display_flush() time.  There might be a small race
with another thread calling wl_display_flush() after our commit request,
but before we flush the DRI driver.  Moving the commit below the DRI
driver flush call looks more natural and eliminates the small race.

Cc: "10.0" mesa-stable@lists.freedesktop.org