pkg/endpoint: specify why local copy of DesiredL4Policy is made
pkg/endpoint: specify why local copy of DesiredL4Policy is made

Signed-off by: Ian Vernon <ian@cilium.io>

tklauser/cilium,cilium-team/cilium,tklauser/cilium,scanf/cilium,scanf/cilium,cilium/cilium,cilium/cilium,tgraf/cilium,eloycoto/cilium,eloycoto/cilium,tgraf/cilium,michi-covalent/cilium,scanf/cilium,michi-covalent/cilium,scanf/cilium,eloycoto/cilium,cilium-team/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,eloycoto/cilium,tklauser/cilium,michi-covalent/cilium,scanf/cilium,tklauser/cilium,tgraf/cilium,eloycoto/cilium,cilium/cilium,scanf/cilium,tklauser/cilium,eloycoto/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,eloycoto/cilium,tgraf/cilium,scanf/cilium