daemon: fix nil pointer when using k8s-prefix
daemon: fix nil pointer when using k8s-prefix

When the user specified a k8s-prefix, the ValidK8sLabelPrefixes was not
initialized resulting in a nil pointer.

Signed-off-by: André Martins <bc9800b9d52a24cce72a73dd528afed53f10e5fc@cilium.io>

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