Dropped flows should identify CPU

**Is your feature request related to a problem? Please describe.**

Recently, we saw an issue where inside a particular node, packets were dropped on a particular CPU. However, kubectl top was not showing CPU running hot (because only few CPUs out of 32 were over burdened). Add the CPU number to the flow extension for drop.

cc: @anubhabMajumdar

Start by tracing the dropped-flow extension in the Go networking observability code and inspect how drop metadata is emitted. Confirm where the CPU identifier should be added, then exercise the existing dropped-flow reporting path and verify that the resulting extension includes the CPU number.

Written by the indexing model from the issue text.