ioctl() calls against a socket with an inappropriate ioctl operation
are incorrectly returning EINVAL rather than ENOTTY:

  [ENOTTY]
      Inappropriate I/O control operation.

This bug causes that when the standard input/output/error of ncurses
are redirected to a socket, it fails to set a NOTTY flag hence sticks
on line-buffered mode,

/* ncurses-5.9/ncurses/tinfo/lib_ttyflags.c */
[...]
            for (;;) {
                if (SET_TTY(termp->Filedes, buf) != 0) {
                    if (errno == EINTR)
                        continue;
                    if ((errno == ENOTTY) && (SP_PARM != 0)) /* fail */
                        SP_PARM->_notty = TRUE;
                    result = ERR;
                }
                break;
            }
[...]

This bug is not limited to socket, it also occurs in a lot of, maybe some
hundred, other ioctl operations, while in the patch I only fixed about a
dozen of additional ones in pipe, fifo and character device drivers.