glx: Fix the GLX_EXT_swap_control_tear drawable attributes
GLX_SWAP_INTERVAL_EXT
is always positive, GLX_LATE_SWAPS_TEAR_EXT
is how
you tell whether the drawable is set to do it. This aligns us with the
spec and NVIDIA's GLX.
Closes: mesa/mesa#10193
Fixes: 5e9e4573835 glx/dri3: Implement GLX_EXT_swap_control_tear