nlmsg_copy_next_header
ifinfo = nlmsg_copy_next_header(hdr, nw, struct ifinfomsg);
ifamsg = nlmsg_copy_next_header(hdr, nw, struct ifaddrmsg);
ndm = nlmsg_copy_next_header(hdr, nw, struct ndmsg);
rtm = nlmsg_copy_next_header(hdr, nw, struct rtmsg);
nlerr = nlmsg_copy_next_header(hdr, nw, struct nlmsgerr);