[NETNS]: Remove empty ->init callback.

The netns start-stop engine can happily live with any of
init or exit callbacks set to NULL.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/ipv6/addrconf.c
Simple merge