unix,tty: don't drain when setting the TTY mode (#4945)

This avoids a blocking syscall (essentially a write)–and thus potential
deadlock–in the asynchronous IO path.

src/unix/tty.c

@@ -333,8 +333,8 @@ int uv_tty_set_mode(uv_tty_t* tty, uv_tty_mode_t mode) {
       UNREACHABLE();
   }
 
-  /* Apply changes after draining */
-  rc = uv__tcsetattr(fd, TCSADRAIN, &tmp);
+  /* Apply changes now, to avoid blocking. */
+  rc = uv__tcsetattr(fd, TCSANOW, &tmp);
   if (rc == 0)
     tty->mode = mode;