pkg/netns: Expand godoc on ReplaceNetNSWithName
pkg/netns: Expand godoc on ReplaceNetNSWithName

It is useful to have an example usage of how ReplaceNetNSWithName() is
typically used so developers don't have to research how to use network
namespaces in Go again.

Signed-off-by: Chris Tarazi <711c73f64afdce07b7e38039a96d2224209e9a6c@isovalent.com>

cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium,cilium/cilium