/net/arp and /net/iproute were world-writable.  Changed to be only
writable by the hostowner (Eve?).

The formal permissions (which were of no effect before, either) are
changed from 666 to:

--rw-rw-r-- I   0 network bootes  0 Oct  6 12:05 /net/arp
--rw-rw-r-- I   0 network bootes  0 Oct  6 12:05 /net/iproute

In fact, only the hostowner can write to them.  (The checking of group
membership is harder than checking ownership for the host).