[PATCH,HURD] Update sysdep/mach/hurd/net/{ethernet.h,if_arp.h,if_ether.h}

[Roland McGrath]

Let's instead move all those linux versions to sysdeps/gnu/net/*.h.
The only difference is <net/ethernet.h> including <net/if_ether.h>
rather than <linux/if_ether.h>.  I think we should give Linux a
net/if_ether.h that just does #include <linux/if_ether.h>, and then
all these other net/*.h files can be common in sysdeps/gnu.


Thanks,
Roland