luci-app-firewall: Fix typo in forwards redirect

When creating a forwarding rule with protocol set to other, a user is
forwarded to the configuration page. The URL for the configuration page
contained a typo - the user was forwarded to
admin/network/firewall/redirect/cfg... and not
admin/network/firewall/forwards/cfg..., leading to a 404.

Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>