policy: Clarify egress policy rule members
policy: Clarify egress policy rule members

- ToCIDR + ToPorts has been supported since #3835 (Cilium v1.1)
- Combining any of the L3 selectors together in a single rule doesn't
  make sense.

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

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