Update callcentric configs to sip.callcentric.net

[matiasgarciaisaia]

Callcentric is updating its network configuration, with a few mandatory changes plus some optional ones: https://www.callcentric.com/faq/51

We should update the domain to sip.callcentric.net, and check if there's anything to do with the IP blocks (I think we don't need to do that, but re-checking won't hurt).

[matiasgarciaisaia]

Since we don't filter Callcentric's IPs in any firewall, there's no need to update IP blocks.

Calls keep working just fine after the deadline.

What we could do is update the domains to sip.callcentric.net.