endpoint: log when regenError is non-nil in Regenerate
endpoint: log when regenError is non-nil in Regenerate

Otherwise, we don't have insight into why the endpoint failed to regenerate via
logs in case producers of the error do not log it.

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

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