net: dynamically allocate fqdir structures

Following patch will add rcu grace period before fqdir
rhashtable destruction, so we need to dynamically allocate
fqdir structures to not force expensive synchronize_rcu() calls
in netns dismantle path.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/proc.c

@@ -72,8 +72,8 @@ static int sockstat_seq_show(struct seq_file *seq, void *v)
 	seq_printf(seq, "RAW: inuse %d\n",
 		   sock_prot_inuse_get(net, &raw_prot));
 	seq_printf(seq,  "FRAG: inuse %u memory %lu\n",
-		   atomic_read(&net->ipv4.fqdir.rhashtable.nelems),
-		   frag_mem_limit(&net->ipv4.fqdir));
+		   atomic_read(&net->ipv4.fqdir->rhashtable.nelems),
+		   frag_mem_limit(net->ipv4.fqdir));
 	return 0;
 }