bp_config: rename fcgi_stock_limit back to fastcgi_stock_limit
bp_config: rename fcgi_stock_limit back to fastcgi_stock_limit

Fixes regression from commit 72151e60afa

CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy,CM4all/beng-proxy