Fix SYN-ACK retransmission bug in accept() causing CI timeouts

[aidangarske]

Descritpion

Fixes test-wolfssl hanging on both Linux and FreeBSD CI due to an orphaned
RTO timer in wolfIP_sock_accept() that prevented SYN-ACK retransmission.

Root Cause

When a SYN arrived at the listening socket:

1. Listening socket transitioned to TCP_SYN_RCVD and got an RTO timer
2. accept() created a new socket and set it directly to TCP_ESTABLISHED
3. Listening socket returned to TCP_LISTEN, orphaning its RTO timer
4. If the SYN-ACK was lost or timing was off → no retransmission → host OS
   connect() timed out → test hung forever

The Fix (src/wolfip.c)

• Keep accepted socket in TCP_SYN_RCVD instead of jumping to TCP_ESTABLISHED;
  the existing ACK handler at lines 3236-3247 completes the transition
• Start RTO timer on the new accepted socket so SYN-ACK gets retransmitted
• Stop the orphaned RTO timer on the listening socket when it returns to TCP_LISTEN
• Defer CB_EVENT_WRITABLE until the final ACK completes the three-way handshake
• Copy negotiated TCP options (window scale, timestamps, SACK, MSS) to the
  accepted socket so the connection starts with correct parameters

Test Changes

• test_native_wolfssl.c: Replace blocking connect() with non-blocking connect
  using select() loop for robustness (matches the pattern in test_eventloop.c)
• unit.c: Add 3 new unit tests verifying RTO timer is active on accepted sockets
  in TCP_SYN_RCVD, stops after the final ACK, and the socket transitions to
  TCP_ESTABLISHED with CB_EVENT_WRITABLE signaled
• unit.c: Fix 3 existing unit test assertions to expect TCP_SYN_RCVD after
  accept() instead of TCP_ESTABLISHED

Test plan

• Unit tests pass locally (517/517, 0 failures)
• Linux CI: test-wolfssl completes without timeout
• FreeBSD CI: test-wolfssl completes without timeout
• macOS CI passes

[Copilot]

Pull request overview

Fixes a TCP accept()/SYN-ACK reliability issue in wolfIP that could leave an orphaned control-RTO timer on the listening socket, preventing SYN-ACK retransmissions and causing CI hangs during host connect().

Changes:

• Update wolfIP_sock_accept() to keep the accepted socket in TCP_SYN_RCVD, start control-RTO on the accepted socket, stop it on the listener, and defer CB_EVENT_WRITABLE until the final ACK.
• Add/adjust unit tests to validate accepted-socket control-RTO behavior and the SYN_RCVD→ESTABLISHED transition on final ACK.
• Make the native wolfSSL test client use non-blocking connect() with a select() loop.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/wolfip.c	Moves accepted sockets to TCP_SYN_RCVD, fixes control-RTO ownership (accepted vs listener), defers writable event signaling.
src/test/unit/unit.c	Adds new tests around accept control-RTO and updates existing assertions for the new post-accept state.
src/test/test_native_wolfssl.c	Switches to non-blocking connect + select() to reduce risk of indefinite blocking in CI.

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