static: T6746: migrate BFD CLI nodes

Migrate "set protocols static route <x.x.x.x/x> next-hop <y.y.y.y> bfd multi-hop
source <z.z.z.z> profile <NAME>" to: "set protocols static route <x.x.x.x/x>
next-hop <y.y.y.y> bfd profile bar"

FRR supports only one source IP address per BFD multi-hop session. VyOS
had CLI cupport for multiple source addresses which made no sense.