NLM_F_APPEND
nl_flags = NLM_F_CREATE | NLM_F_APPEND; /* Do append by default */
hdr->nlmsg_flags &= ~(NLM_F_EXCL | NLM_F_APPEND);
op_flags |= (nlm_flags & NLM_F_APPEND) ? RTM_F_APPEND : 0;