plugins/loopback: return empty result
plugins/loopback: return empty result

This is needed to conform to the specification and allow successful
unmarshalling in the invoker.

tangle329/cni,squeed/plugins,tomdee/cni,aanm/cni,containernetworking/cni,aanm/cni,steveeJ/cni,luxas/cni,dcbw/cni,containernetworking/plugins,jonboulle/cni,containernetworking/plugins,squeed/plugins,achanda/cni,kad/cni,jonboulle/cni,appc/cni,achanda/cni,dcbw/cni,mcastelino/cni,luxas/cni,squaremo/cni,appc/cni,tomdee/cni,steveeJ/cni,rosenhouse/cni,murat1985/cni,containernetworking/cni,tangle329/cni,kad/cni,squaremo/cni,mcastelino/cni,murat1985/cni,rosenhouse/cni