net: neighbour table ABI problem

The neighbor table time of last use information is returned in the
incorrect unit. Kernel to user space ABI's need to use USER_HZ (or
milliseconds), otherwise the application has to try and discover the
real system HZ value which is problematic.  Linux has standardized on
keeping USER_HZ consistent (100hz) even when kernel is running
internally at some other value.

This change is small, but it breaks the ABI for older version of
iproute2 utilities.  But these utilities are already broken since they
are looking at the psched_hz values which are completely different. So
let's just go ahead and fix both kernel and user space. Older
utilities will just print wrong values.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>