tty: document @dlci parameter in gsm_modem_send_initial_msc

tty: document @dlci parameter in gsm_modem_send_initial_msc

Add missing kernel-doc entry for the @dlci parameter in
gsm_modem_send_initial_msc(), which fixes the following warning
reported by kernel-doc:

Warning: drivers/tty/n_gsm.c:4175 function parameter 'dlci' not described in 'gsm_modem_send_initial_msc'

Signed-off-by: Kriish Sharma <kriish.sharma2006@gmail.com>
Link: https://patch.msgid.link/20251025161206.795784-1-kriish.sharma2006@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>