ssping: use close+recreate instead of connect(AF_UNSPEC) for reliable TCP cleanup

[Copilot]

connect(AF_UNSPEC) on TCP sockets is a Linux-specific tcp_disconnect() extension that does not reliably send RST/FIN in all connection states, leaving stale TCP state at the remote end.

Replace with close() + fresh socket() which guarantees FIN delivery for established connections and proper kernel cleanup for SYN_SENT.

• fd_ssping.c — remove_fdesc_idx() now closes the socket and creates a fresh nonblocking TCP socket with TCP_NODELAY, instead of attempting connect(AF_UNSPEC)
• fd_snapct_tile.seccomppolicy — Allow close and setsockopt(TCP_NODELAY) on ping fds (previously blocked to match the socket-reuse design)
• fd_snapct_tile_seccomp.h — Regenerated (8 fewer BPF instructions from removed ping fd range exclusions)

/* Before: non-standard, unreliable on TCP */
connect( fdesc, &(struct sockaddr_in){ .sin_family = AF_UNSPEC }, ... );

/* After: standard close sends FIN, then fresh socket for reuse */
close( fdesc );
fdesc = socket( AF_INET, SOCK_STREAM|SOCK_NONBLOCK, 0 );
setsockopt( fdesc, SOL_TCP, TCP_NODELAY, &tcp_nodelay, sizeof(int) );

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