BUILD: threads: add the definition of PROTO_LOCK

This one was added by commit daacf3664 ("BUG/MEDIUM: protocols: add a
global lock for the init/deinit stuff") but I forgot to add it to the
include file, breaking DEBUG_THREAD.

(cherry picked from commit d6e0c03384cab2c72fb6ab841420045108ea4e6f)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
1 file changed