Disable/Enable SIP ALG

@alzhao
Hi,
one of my Mini-Routers is the GL-AR300M-16 and is dedicated to manage my Home LAN.
Using an ethernet switch I have connected an ATA Linksys PAP2T-NA for VoIP management.
Reading this page I was able to verify that SIP ALG is anabled in my Mini-Router.
After many days of testing I have ascertained that the VoIP problems are due to SIP ALG.
I was able to disable SIP ALG (only) temporarily and as long as it is disabled my VoIP works perfectly,
but once the router is rebooted or surprisingly even after a few hours of operation even without rebooting the two modules “nf_conntrack_sip” and “nf_nat_sip” are still there enabling again SIP ALG with the consequence that my VoIP stop working again.
I have tried with the command:

modprobe -r nf_conntrack_sip

…but OpenWRT seem don’t accept the -r option

So I have tried with rmmod…

modinfo nf_conntrack_sip

modinfo nf_nat_sip

rmmod /lib/modules/4.14.241/nf_conntrack_sip.ko

unloading the module failed

rmmod /lib/modules/4.14.241/nf_nat_sip.ko

so I was able to remove temporarly only the second one.

I was not able to find any /etc/rc.module or /etc/rc.modules

Maybe would be possible to comment with “nano” the module name in a file like above to remove from loading in kernel?
but where is the file?

I’m not familiar at all with system administration so I would really appreciate if you could write me down step by step the command lines to definitely remove this two modules from loading in kernel.
Thank you in advance.