pkg/utils: use constant for chain prefix
pkg/utils: use constant for chain prefix

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