* [bgpcfgd]: Generate set src configuration dynamically
Sometimes zebra starts faster then swss configures Loopback0
In this case "set src" inside of the route map will not be
inserted to the configuration because zebra doesn't see Loopback
ips in the list of available ip addresses.
I've added extra logic to push the "set src" configuration only
when Loopback has been configured by swss.
