llcp_add_header
skb = llcp_add_header(skb, sock->dsap, sock->ssap, cmd);
skb = llcp_add_header(skb, 0, 0, LLCP_PDU_SYMM);
skb = llcp_add_header(skb, LLCP_SAP_SDP, LLCP_SAP_SDP, LLCP_PDU_SNL);
skb = llcp_add_header(skb, dsap, ssap, LLCP_PDU_DM);
pdu = llcp_add_header(pdu, dsap, ssap, LLCP_PDU_UI);