When multiple IP addresses are configured for a single
interface, this object is used to determine which address
is the 'primary' address. 'Primary' addresses are used
as the source IP address in packets sent from that
interface. When there is only one address configured for
an interface, it will be the 'primary' address. If there
is an existing 'primary' address when this object is set
to primary (1), the existing 'primary' address will be
set to 'secondary' automatically.