tty: n_gsm: fix wrong DLCI release order

The current DLCI release order starts with the control channel followed by
the user channels. Reverse this order to keep the control channel open
until all user channels have been released.

Fixes: e1eaea46

 ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220414094225.4527-9-daniel.starke@siemens.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>