patch 8.2.0774: t_TI and t_TE are output when using 'visualbell'

Problem:    t_TI and t_TE are output when using 'visualbell'. (Dominique
            Pelle)
Solution:   Do not change the terminal mode for a short sleep.  Do not output
            t_TI and t_TE when switching to/from TMODE_SLEEP. Make tmode an
            enum.
diff --git a/src/proto/os_unix.pro b/src/proto/os_unix.pro
index b9db0fc..cb84994 100644
--- a/src/proto/os_unix.pro
+++ b/src/proto/os_unix.pro
@@ -48,7 +48,7 @@
 void mch_early_init(void);
 void mch_free_mem(void);
 void mch_exit(int r);
-void mch_settmode(int tmode);
+void mch_settmode(tmode_T tmode);
 void get_stty(void);
 int get_tty_info(int fd, ttyinfo_T *info);
 void mch_setmouse(int on);