Refactor: notify_client to no longer rely on global booth_conf var

Consequently, foreach_tkt_req (what said function is ultimately passed
into) that practically implements high order functional do-for-all
pattern with the same subset of arguments that itself receives, needs
to be extended with this extra argument as well.

Also, apply the same recursively to superjacent call graph expansion
(progression up to main.c).

Also mark function being effectively static.

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>