BUG/MINOR: stick-table: cap sticky counter idx with tune.nb_stk_ctr instead of MAX_SE...

BUG/MINOR: stick-table: cap sticky counter idx with tune.nb_stk_ctr instead of MAX_SESS_STKCTR

Cap sticky counter index with tune.nb_stk_ctr instead of MAX_SESS_STKCTR for
sc-add-gpc. Same logic is already implemented for sc-inc-gpc and sc-set-gpt
keywords. So, it seems missed for sc-add-gpc.

This fixes the issue #3061 reported at GitHub. Thanks to @ma311 for
reporting their analysis of the issue.
This should be backported in all versions until 2.8, included 2.8.

(cherry picked from commit 21d5f43aa6e9513d11dff2d80a2a332d92c0a857)
Signed-off-by: Amaury Denoyelle <adenoyelle@haproxy.com>
(cherry picked from commit 4b71a4c528876a37fee996ac1326b03622c90bc7)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>