Building kmod-ipt-nathelper-rtsp

My ISP is using a custom OpenWRT (OverTheBox

And I need to acess RTSP on the router behind OpenWRT, because they do not provide all kmod I build it from the git with CONFIG_ALL_KMODS=y but I do not get any ip_conntrack_rtsp.ko built and thus no correponding ipk

Can you tell me what i'm doing wrong and how to build this file ?