. moved the global variables llc_ind_prim and llc_cfm_prim
  to struct llc_sap, to make the code reentrant
. one kerneldoc comment for a struct
. created llc_pdu_{s,u}n_hdr and llc_set_pdu_hdr to abstract
  access to skb internals (skb->nh.raw)
. renamed llc_get_llc_hdr_length to llc_get_hdr_len and simplify it
. killed some uneeded variables in llc_sap_send_ev