tty: n_gsm: add copyright Siemens Mobility GmbH

More than 1/3 of the n_gsm code has been contributed by us in the last
1.5 years, completing conformance with the standard and stabilizing the
driver:
- added UI (unnumbered information) frame support
- added PN (parameter negotiation) message handling and function support
- added optional keep-alive control link supervision via test messages
- added TIOCM_OUT1 and TIOCM_OUT2 to allow responder to operate as modem
- added TIOCMIWAIT support on virtual ttys
- added additional ioctls and parameters to configure the new functions
- added overall locking mechanism to avoid data race conditions
- added outgoing data flow to decouple physical from virtual tty handling
for better performance and to avoid dead-locks
- fixed advanced option mode implementation
- fixed convergence layer type 2 implementation
- fixed handling of CLD (multiplexer close down) messages
- fixed broken muxer close down procedure
- and many more bug fixes

With this most of our initial RFC has been implemented. It gives the driver
a quality boost unseen in the decade before.

Add a copyright notice to the n_gsm files to highlight this contribution.

Link: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Daniel Starke <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/n_gsm.c

···
 /*
  * n_gsm.c GSM 0710 tty multiplexor
  * Copyright (c) 2009/10 Intel Corporation
+ * Copyright (c) 2022/23 Siemens Mobility GmbH
  *
  *	* THIS IS A DEVELOPMENT SNAPSHOT IT IS NOT A FINAL RELEASE *
  *

include/uapi/linux/gsmmux.h

···
 /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/* Copyright (c) 2022/23 Siemens Mobility GmbH */
 #ifndef _LINUX_GSMMUX_H
 #define _LINUX_GSMMUX_H