hubble: Document purpose of cancellation context
hubble: Document purpose of cancellation context

The cancel() looks potentially unused in the local observer code here,
so added a comment indicating how it's used and why the cancellation is
there at all.

Signed-off-by: Chance Zibolski <0671e890c734ee0cb7f0027fb3ef2496c29582eb@gmail.com>

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