(struct net *)->ipv4.fqdir will soon be a pointer, so make
sure ip4_frags_ns_ctl_table[] does not reference init_net.

ip4_frags_ns_ctl_register() can perform the needed initialization
for all netns.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>