BUG/MINOR: cache: Inverted variables in http_calc_maxage function

BUG/MINOR: cache: Inverted variables in http_calc_maxage function

The maxage and smaxage variables were inadvertently assigned the
Cache-Control s-maxage and max-age values respectively when it should
have been the other way around.

This can be backported on all branches after 1.8 (included).

(cherry picked from commit 8c2db71326addbcf9d6c8ae4d2048247031f9e4c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 2185f7e2b809889310efdf087da6777583607597)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>