endpoint: Document SelectorCache notification
endpoint: Document SelectorCache notification

Document why the endpoint's AllocateIdentity() function triggers
notification into the SelectorCache and yet the Release does not.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@cilium.io>

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