WPS: Add prefixes to public event_* functions

WPS: Add prefixes to public event_* functions

openssl engines may dynamically load external libraries. Our event_*()
functions happen to be named very generically, such that event_add()
collides with the libevent library (https://libevent.org/). This can
have disastrous effects (esp. when using CONFIG_WPA_TRACE, which enables
partial linking) when our SSL engines call into the WPS event_add()
instead of their intended libevent event_add().

Resolve this by providing a more unique prefix to these functions.

Rename performed via:

  sed -i -E \
    's:\<event_(add|delete_all|send_all_later|send_stop_all)\>:wps_upnp_event_\1:g' \
     $(git grep -l event_)

Tested via (among other things) hwsim '-f ap_wps' module.

Signed-off-by: Brian Norris <briannorris@chromium.org>