tty: n_gsm: fix missing update of modem controls after DLCI open

tty: n_gsm: fix missing update of modem controls after DLCI open

[ Upstream commit d6c9b0b8950dee99f2611bfd68bf7d6f65ab491d ]

Currently the peer is not informed about the initial state of the modem
control lines after a new DLCI has been opened.
Fix this by sending the initial modem control line states after DLCI open.

Fixes: 99551fa31543 ("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/20220420101346.3315-1-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>