isdn/gigaset: bas_gigaset timer cleanup

Use setup_timer() and mod_timer() instead of direct assignment to
timer structure members, simplify the argument of one timer routine,
and make extra sure all timers are stopped during suspend.

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>