Refine type of lladdr_pton() and lladdr_ntop()

It also makes Ethernet addresses with a single octect valid.
Adjust constants

AF_XIA had to change due to the recent introduction of AF_VSOCK
in the kernel.

kernel-include/linux/rtnetlink.h had to be updated because
RTA_LLADDR changed due to the introduction of RTA_MFC_STATS.

Change XDP type to harmonize Linux and Click XIA.