vrrp: Allow a static_ipaddress to enable an interface to leave fault state

If the interface of a VRRP instance does not have an IP address, then
the VRRP instance will be put into fault state. However, if the
configuration has a static_ipaddress for that interface, then that
should be sufficient for the VRRP instance to leave fault state.

This commit allow static_ipaddresses to be considered to be the
primary address of an interface, and hence allow a VRRP instance to come up.

Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>