Parent: #1488

Augment the BPF datapath to be able to handle label-based egress. This will consist of reading from a table that is populated by the Cilium agent with pod IPs to which egress traffic is allowed.

• Add an IP->SecID mapping table to BPF (Datapath portion of egress label-based policy enforcement #2954)
• Add Label-based lookup to the map, following the example of ingress policy map (Datapath portion of egress label-based policy enforcement #2954)
• Refactor the existing L4 port policy from code to a native BPF map (L4-only) (Extend BPF policymap to include proxy_port #2918)
• Extra wishlist items, but not required to implement:
  • Userspace - populate maps with proxy_port (Shift proxy_port datapath handling from embedded BPF_L4_MAP into native POLICY_MAP #2564)
  • Userspace - atomic map replace