This patch adds a bit in in_ifaddr.ifa_flag (IFA_F_NO_NDISC). If it is
set, the host doesn't answer to the neighbour's discovery request
for this address. Currently it is honored only by ipv4/arp.

This feature is usefull to support VRRP(rfc2338) which requires
to answer the ARP request for a 'virtual ip' with the proper
'virtual MAC'(rfc2338 section 8.2). So to potentially answer 
a particular MAC for a particular IP, and not with the primary
MAC. As far as i know currently, linux assumes to have a single
MAC per physical interface. My plan is to prevent the kernel
from answering for the virtual ip addresses and to answer 
from userspace.

It is the less intrusive solution i found to support several
'virtual routers' per physical interface. My vrrpd implementation
runs entirely in userspace but without this feature it can't support 
several virtual routers per physical interface.

I am not sure that read_lock(&in_dev->lock) in inet_ifa_bylocal()
is the good way to lock but it seems the most reasonable to me.
please correct me if needed.

The patch is in 2 parts:
        o the kernel 2.4.0-test1 modifications
        o the iproute2-2.2.4-now-ss000305 modifications to set/report
          the no_ndisc bit from userspace.