Expose TCP statistics helpers (bpf_tcp_sock() helper)

Nobody has claimed this yet.

[RFC 4898](https://datatracker.ietf.org/doc/html/rfc4898) defines TCP Extended Statistics, which Windows has supported since Vista as exposed in via [GetPerTcpConnectionEStats()](https://docs.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getpertcpconnectionestats) and [GetPerTcp6ConnectionEStats()](https://docs.microsoft.com/en-us/windows/win32/api/iphlpapi/nf-iphlpapi-getpertcp6connectionestats).

Some iphlpapi functionality is exposed in kernel mode netioapi.h as discussed at https://docs.microsoft.com/en-us/windows-hardware/drivers/network/ip-helper but currently this is not exposed.

Windows also supports a socket ioctl [SIO_TCP_INFO](https://docs.microsoft.com/en-us/windows/win32/winsock/sio-tcp-info) with basic TCP stats but they are only available to a process with the socket handle.

Does Linux support TCP EStats or TCP basic stats?

Start by comparing the kernel-mode netioapi.h surface with the bpf_tcp_sock() helper, GetPerTcpConnectionEStats(), GetPerTcp6ConnectionEStats(), and SIO_TCP_INFO mentioned in the issue. Determine whether Linux provides equivalent TCP extended or basic statistics and define the scope of exposing them; done means the supported API surface and implementation requirements are agreed.

Written by the indexing model from the issue text.