bpf: LivenessScanner only deletes the current key
bpf: LivenessScanner only deletes the current key

It may lookup the reverse key when it hits a forward entry, but it must
not delete it at that time.

Metaswitch/calico,Metaswitch/calico,neiljerram/felix,neiljerram/felix,neiljerram/felix,neiljerram/felix