spanstat: refactor negative duration check
spanstat: refactor negative duration check

Use "safetime.TimeSinceSafe" which checks for and logs a negative duration.

Signed-off-by: Martynas Pumputis <b14a8f953b021d09d1aafdca53cb27d7d9cede0c@covalent.io>

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