tty: n_gsm: add restart flag to extended ioctl config

tty: n_gsm: add restart flag to extended ioctl config

Currently, changing the parameters of the n_gsm mux gives no direct control
to the user whether this should trigger a mux reset or not. The decision is
solely made by the driver based on the assumption which parameter changes
are compatible or not. Therefore, the user has no means to perform an
automatic mux reset after parameter configuration for non-conflicting
changes.

Add the parameter 'flags' to 'gsm_config_ext' to force a mux reset after
ioctl setting regardless of whether the changes made require this or not
by setting this to 'GSM_FL_RESTART'. This is done similar to
'GSM_FL_RESTART' in gsm_dlci_config.flags.

Note that 'GSM_FL_RESTART' is currently the only allowed flag to allow
additions here.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20230817093231.2317-9-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>