vrrpd: properly find iface in manual cfg mode

vrrpd: properly find iface in manual cfg mode

As a crutch, interface search when manually configuring VRRP on an
interface did a prefix match on the name of macvlan interfaces,
comparing its name to the name of the interface VRRP was configured on
in order to determine if the interface under question was a subinterface
of the configured interface. This is obviously fragile and prone to
failure. We now pass up parent interface info from Zebra so use that
instead to correctly deduce parent-child relationships.

Signed-off-by: Quentin Young <qlyoung@cumulusnetworks.com>