endpoint: document when mutex not needed for updating logger
endpoint: document when mutex not needed for updating logger

The endpoint mutex does not need to be acquired if the fields parameter is non-nil when calling
`endpoint.UpdateLogger()`, so document it accordingly.

Signed-off by: Ian Vernon <ian@cilium.io>

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