networking: add 'ip neigh' command

networking: add 'ip neigh' command

This patch ports the 'ip neigh' command, originally written by Alexey
Kuznetsov, <kuznet@ms2.inr.ac.ru>, to busybox.

The base of the port is the version of iproute that shipped with
Debian Squeeze, taken from:

  http://http.debian.net/debian/pool/main/i/iproute/iproute_20100519.orig.tar.gz

This patch has actively been used by the Open Network Install
Environment (ONIE) project for over 3 years without incident.

function                                             old     new   delta
print_neigh                                            -     933    +933
ipneigh_list_or_flush                                  -     742    +742
get_hz                                                 -     109    +109
do_ipneigh                                             -      62     +62
do_iproute                                          2112    2153     +41
packed_usage                                       30647   30667     +20
ipneigh_main                                           -      14     +14
static.ip_neigh_commands                               -      12     +12
static.nuds                                            -       9      +9
static.ip_func_ptrs                                   32      36      +4
print_route                                         1858    1727    -131
------------------------------------------------------------------------------
(add/remove: 8/0 grow/shrink: 3/1 up/down: 1946/-131)        Total: 1815 bytes

Signed-off-by: Curt Brune <curt@cumulusnetworks.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>