Returns the options set on a socket.
    The $QIO equivalent is the IO$_SENSEMODE function.
    Format
      #include  <types.h>
      #include  <socket.h>
      int getsockopt  ( int s, int level, int optname, char *optval,
                      int *optlen ); (_DECC_V4_SOURCE)
      int getsockopt  ( int s, int level, int optname, void *optval,
                      size_t *optlen ); (not_DECC_V4_SOURCE)