Add a new way to configure the preferred source address when talking to
remote servers such as primaries and parental-agents. This will
eventually deprecate options such as 'parental-source',
'parental-source-v6', 'transfer-source', etc.
Example of the new configuration:
parental-agents "parents" port 5353 \
source 10.10.10.10 port 5354 dscp 54 \
source-v6 2001:db8::10 port 5355 dscp 55 {
10.10.10.11;
2001:db8::11;
};
ad248f2261