[PATCH] isdn4linux: Gigaset base driver: improve error recovery

The following patch to the Siemens Gigaset base driver adds graceful
recovery for some frequently encountered error conditions, by retrying
failed control requests (eg.  stalled control pipe), and by closing and
reopening the AT command channel when it appears to be stuck.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Acked-by: Hansjoerg Lipp <hjlipp@web.de>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>