This adds ARPHRD_NETLINK to ll_types so that it can be properly
shown e.g. in `ip a`:

 8: nlmon: <NOARP,UP,LOWER_UP> mtu 3776 qdisc noqueue state UNKNOWN group default
    link/netlink
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>