CTL_NET_IPv4_ADDR_t ctl_dns_get_server(unsigned index);
ctl_dns_get_server returns the IP address of the DNS server with index index. If index is invalid, ctl_dns_get_server returns an all-zero IP address.
If IP addresses are assigned by DHCP, ctl_dns_get_server returns all-zero IP address whilst IP negotiation is in progress.