#513 spectranet socket interrupts

[Guesser]

There are two w5100 socket interrupts not being raised when they should which breaks the spectranet BASIC channels and streams module:

• The 'CON' interrupt when switching to W5100_SOCKET_STATE_ESTABLISHED in w5100_socket_process_accept
• 'DISCON' when switching to W5100_SOCKET_STATE_CLOSE_WAIT in w5100_socket_process_read.

This prevents software detecting connect/disconnect events until data is received and a read fails.

I haven't exhaustively tested different states so there may be other conditions which differ from the hardware behaviour.