Daemons like staticd already implement nexthop zapi (un)registration.
b7ca809d1c ("lib: BFD automatic source selection") has implemented a
concurrent nexthop (un)registration. Some nexthop could be unregistred
by the bfd whereas they were still needed by the daemon.
Let the deamons deal with nexthop zapi (un)registration.
Fixes: b7ca809d1c ("lib: BFD automatic source selection")
Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>