libwebsockets

optimize utf8 check tests into state bit

Considering we go through it once per incoming char, the tests to see if we
should be checking utf-8 are too expensive... move them to a bit that lives
in the wsi and set them once per frame (except for CLOSE who has to update
after the close code has been skipped).

Signed-off-by: Andy Green <andy.green@linaro.org>