net: neighbour: fix neigh_dump_info()

[ Upstream commit 4bd6683bd400c8b1d2ad544bb155d86a5d10f91c ]

Denys found out "ip neigh" output was truncated to
about 54 neighbours.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Denys Fedoryshchenko <denys@visp.net.lb>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>