bpf_host: describe the position of {to,from}-{host,netdev} in the data path
bpf_host: describe the position of {to,from}-{host,netdev} in the data path

Add some comments about when and where exactly the BPF host entrypoints are
attached to.

Signed-off-by: Timo Beckers <98c2d5a1e48c998bd9ba9dbc53d6857beae1c9bd@isovalent.com>

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