Accepts a connection on a passive socket.
    The $QIO equivalent is the IO$_ACCESS system service with the
    IO$M_ACCEPT modifier.
    Format
      #include  <types.h>
      #include  <socket.h>
      int accept  ( int s, struct sockaddr *addr, int *addrlen );
                  (_DECC_V4_SOURCE)
      int accept  ( int s, struct sockaddr *addr, size_t *addrlen );
                  (not_DECC_V4_SOURCE)