Sockets Added Sockmap Socket Interface

Added a :ref:sockmap socket interface <envoy_v3_api_msg_extensions.network.socket_interface.sockmap.v3.Sockmap> that accelerates same-host TCP hops with eBPF. A sock_ops program tracks established local sockets in a BPF_MAP_TYPE_SOCKHASH and an sk_msg program redirects their payloads with bpf_msg_redirect_hash, bypassing the kernel TCP/IP stack. It is available on Linux only and requires a kernel 4.18 or later. Connections whose peer is not on the same host transparently fall back to TCP/IP.