policy: Expand comments for policy objects
policy: Expand comments for policy objects

Describe in more detail what `L4Policy` and `L3L4Policy` are.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@covalent.io>

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