tty: n_gsm: Fix control dlci ADM mode processing

tty: n_gsm: Fix control dlci ADM mode processing

Currently, code retries n2 times to open control dlci in ABM mode before
switching to ADM mode, but only if DM has been received. This contradicts
to the comment that dlci is switched to control mode unconditionally if
DLCI_OPENING retries time out. Also, it does not make sense to continue
trying once DM has received.

Change the logic to switch to ADM mode upon DM received. That way control
channel state will change to DLCI_OPEN way faster. Fix the misleading
comment while at it.

Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20241228150100.100354-3-ivo.g.dimitrov.75@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>