There was a possible recursion that could eventually overflow the stack. The...

There was a possible recursion that could eventually overflow the stack.  The error occurred when closing the socket with inet_close() while a socket callback was still queued.  When the socket callback was executed by devif_conn_event(), this resulted in a call to psock_send_eventhandler() with TCP_CLOSE flag set which then called tcp_lost_connection().  tcp_shutdown_monitor() then called tcp_callback() again, which again called psock_send_eventhandler(), and so on....  Noted by Pascal Speck.  Solution is also similar to a solution proposed by Pascal Speck.