[LLC]: Make llc_frame_alloc take a net_device as an argument

So as to set the newly created sk_buff ->dev member with it, that way we stop
using dev_base->next, that is the wrong thing to do, as there may well be
several interfaces being used with LLC. This was not such a big problem after
all as most of the users of llc_alloc_frame were setting the correct dev, but
this way code is reduced.

This also fixes another bug in llc_station_ac_send_null_dsap_xid_c, that was
not setting the skb->dev field.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>