n_tty: update comment for WAKEUP_CHARS define

Give a better descriptions of what WAKEUP_CHARS represents.
Signed-off-by: Valentin Vidic <Valentin.Vidic@CARNet.hr>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -50,8 +50,10 @@
 #include <linux/ratelimit.h>
 #include <linux/vmalloc.h>
 
-
-/* number of characters left in xmit buffer before select has we have room */
+/*
+ * Until this number of characters is queued in the xmit buffer, select will
+ * return "we have room for writes".
+ */
 #define WAKEUP_CHARS 256
 
 /*