o LLC: trim down llc_core to the very basic support needed by IPX et all

o LLC: trim down llc_core to the very basic support needed by IPX et all

Renaming the basic support module to llc.ko and introducing llc_core.c,
that has just the basic output path for llc_build_and_send_ui_pkt.

Next step will be to rename llc_main.c to llc_station.c, then consolidate
all the llc station code in this file, removing all the not needed
llc_station parameters and killing struct llc_station altogether,
no sense in having it as there is just one station, always. BTW in
this changeset parts of llc_main_station was already moved to llc_core.c,
namely the sap list and lock.