net: TCP sockets in the kernel - a Game Boy fetches HTTP over real TCP

Kernel TCP client on the socket layer: net_connect(SOCK_TCP) runs the 3-way
handshake in-kernel, send()/recv() drive the byte stream, close() does the FIN.

- Socket gains state + 32-bit snd_nxt/rcv_nxt (big-endian, add-with-carry-fold).
- tcp_send_seg builds IP+TCP with a pseudo-header checksum; the SYN carries an
  MSS option (200) so the peer never sends a segment larger than our 256-byte
  frame buffer (we don't do IP reassembly).
- tcp_in state machine: SYN_SENT->ESTABLISHED on SYN-ACK, buffers in-order data
  and ACKs it, handles FIN -> recv() returns 0 (EOF).
- No retransmission: the GB<->host link is lossless and the host's real TCP
  owns the internet side - which removes TCP's hardest part.
- net_pump now processes one frame per call so recv drains each segment before
  the next arrives (single rx slot, no overwrite).

wget.c is now a thin socket client: connect -> send "GET / HTTP/1.0" -> recv to
EOF -> print. Verified end to end against a host HTTP server:

    /# wget 10.0.0.1
    HTTP/1.0 200 OK
    Hello from a real HTTP server, fetched by a Game Boy!

with a clean SYN/SYN-ACK/ACK ... PSH ... FIN/ACK trace on the wire.

0 files changed, 0 insertions, 0 deletions