[ISDN]: i4l: Fix DLE handling for i4l-audio

The DLE handling in i4l-audio seems to be broken.

It produces spurious DLEs so asterisk 1.2.24 with chan_modem_i4l
gets irritated, the error message is:
"chan_modem_i4l.c:450 i4l_read: Value of escape is ^ (17)".
-> There shouldn't be a DLE-^.
If a spurious DLE-ETX occurs, the audio connection even dies.
I use a "AVM Fritz!PCI" isdn card.

I found two issues that only appear if ISDN_AUDIO_SKB_DLECOUNT(skb) > 0:
- The loop in isdn_tty.c:isdn_tty_try_read() doesn't escape a DLE if it's
  the last character.

- The loop in isdn_common.c:isdn_readbchan_tty() doesn't copy its characters,
  it only remembers the last one ("last = *p;").

  Compare it with the loop in isdn_common.c:isdn_readbchan(), that *does*
  copy them ("*cp++ = *p;") correctly.
  The special handling of the "last" character made it more difficult.
  I compared it to linux-2.4.19: There was no "last"-handling and both loops
  did escape and copy all characters correctly.
Signed-off-by: Matthias Goebl <matthias.goebl@goebl.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/i4l/isdn_common.c

@@ -914,6 +914,9 @@ isdn_readbchan_tty(int di, int channel, struct tty_struct *tty, int cisco_hack)
 			dflag = 0;
 			count_pull = count_put = 0;
 			while ((count_pull < skb->len) && (len > 0)) {
+				/* push every character but the last to the tty buffer directly */
+				if ( count_put )
+					tty_insert_flip_char(tty, last, TTY_NORMAL);
 				len--;
 				if (dev->drv[di]->DLEflag & DLEmask) {
 					last = DLE;

drivers/isdn/i4l/isdn_tty.c

@@ -85,6 +85,8 @@ isdn_tty_try_read(modem_info * info, struct sk_buff *skb)
 								tty_insert_flip_char(tty, DLE, 0);
 							tty_insert_flip_char(tty, *dp++, 0);
 						}
+						if (*dp == DLE)
+							tty_insert_flip_char(tty, DLE, 0);
 						last = *dp;
 					} else {
 #endif