bpf: avoid hitting global map update spinlock for udp services
bpf: avoid hitting global map update spinlock for udp services

Same reasoning as with a63035340b4f ("bpf: only update nodeport neigh
entry if stale or non-existant"). For sock LB users with UDP proto, this
map update is in the hot-path and constantly hitting the map update
spinlock which is completely unnecessary and very high overhead. Only
update if needed.

Signed-off-by: Daniel Borkmann <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@iogearbox.net>

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