k8s: Consistently check for namespace labels in endpoint selectors
k8s: Consistently check for namespace labels in endpoint selectors

Some checks were only looking for the K8s namespace label in
matchLabels, wheras others were looking in both matchLabels and
matchExpressions.  Make it consistent by doing only the latter.

Signed-off-by: Romain Lenglet <b8aabb4b95c817d9df69b6be95b2b94d6b1efe17@covalent.io>

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