tty: move N_TTY_BUF_SIZE to n_tty

"N_TTY_BUF_SIZE" is private to n_tty and shall not be exposed to the
world. Definitely not in tty.h somewhere in the middle of "struct
tty_struct".

This is a remnant of moving "read_flags" to "struct n_tty_data" in
commit 3fe780b379fa ("TTY: move ldisc data from tty_struct: bitmaps").
But some cleanup was needed first (in previous patches).

Signed-off-by: Jiri Slaby (SUSE) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/n_tty.c

···
  */
 #define WAKEUP_CHARS 256
 
+#define N_TTY_BUF_SIZE 4096
+
 /*
  * This defines the low- and high-watermarks for throttling and
  * unthrottling the TTY driver.  These watermarks are used for

include/linux/tty.h

···
 
 	struct list_head tty_files;
 
-#define N_TTY_BUF_SIZE 4096
 	struct work_struct SAK_work;
 } __randomize_layout;