tests: Use "NAT46" term consistently.
tests: Use "NAT46" term consistently.

It was confusing when "nat64" and "nat46" were used
interchangeably. Change to consistently use "NAT46".

Signed-off-by: Jarno Rajahalme <0f1ab0ac7dffd9db21aa539af2fd4bb04abc3ad4@covalent.io>

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