node-neigh: Skip neigh update if arping is stale
node-neigh: Skip neigh update if arping is stale

It's possible that in the case of multiple concurrent insertNeighbor()
executions the oldest (or older) goroutine will overwrite the latest
arping result due to the fine-grained locking.

To fix this, avoid updating neigh entry if we detect that prev last ping
timestamp is after our arping timestamp.

Signed-off-by: Martynas Pumputis <6b0d31c0d563223024da45691584643ac78c96e8@lambda.lt>

cilium/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium