CentOS dropped CentOS 6 support years ago.
Anyone running Kamailio on CentOS 6 is most likely not updating their Kamailio either. If you pay Redhat for extended support, you've got another year of RHEL6. Those users can run a mildly older branch of Kamailio until that day comes. Kamailio 5.7.x
I am saying this as someone this would affect. Drop us.