tty: n_gsm: add parameters used with parameter negotiation

n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516


The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to
the newer 27.010 here. Chapter 5.4.6.3.1 describes the encoding of the
parameter negotiation messages.

Add the parameters used there to 'gsm_mux' and 'gsm_dlci' and initialize both
according to the value ranges and recommended defaults defined in chapter 5.7.

Replace the use of the DLC default values from the 'gsm_mux' fields with the DLC
specific values from the 'gsm_dlci' fields where applicable.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20221103091743.2119-2-daniel.starke@siemens.com


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