tty: n_gsm: Demote obvious abuse of kernel-doc and supply other missing docss

Fixes the following W=1 kernel build warning(s):

drivers/tty/n_gsm.c:85: warning: Function parameter or member 'ref' not described in 'gsm_mux_net'
drivers/tty/n_gsm.c:85: warning: Function parameter or member 'dlci' not described in 'gsm_mux_net'
drivers/tty/n_gsm.c:664: warning: Function parameter or member 'dlci' not described in 'gsm_data_kick'
drivers/tty/n_gsm.c:1015: warning: Function parameter or member 'clen' not described in 'gsm_process_modem'

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/n_gsm.c

···
 #define MAX_MTU 1500
 #define	GSM_NET_TX_TIMEOUT (HZ*10)
 
-/**
+/*
  *	struct gsm_mux_net	-	network interface
  *
  *	Created when net interface is initialized.
···
 /**
  *	gsm_data_kick		-	poke the queue
  *	@gsm: GSM Mux
+ *	@dlci: DLCI sending the data
  *
  *	The tty device has called us to indicate that room has appeared in
  *	the transmit queue. Ram more data into the pipe if we have any
···
  *	@tty: virtual tty bound to the DLCI
  *	@dlci: DLCI to affect
  *	@modem: modem bits (full EA)
+ *	@clen: command length
  *
  *	Used when a modem control message or line state inline in adaption
  *	layer 2 is processed. Sort out the local modem state and throttles