net: af_unix can make unix_nr_socks visbile in /proc

Currently, /proc/net/protocols displays socket counts only for TCP/TCPv6
protocols

We can provide unix_nr_socks for free here, this counter being
already maintained in af_unix

Before patch :

# grep UNIX /proc/net/protocols
UNIX       428     -1      -1   NI       0   yes  kernel

After patch :

# grep UNIX /proc/net/protocols
UNIX       428     98      -1   NI       0   yes  kernel
Signed-off-by: NEric Dumazet <dada1@cosmosbay.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/unix/af_unix.c

@@ -568,6 +568,7 @@ static const struct proto_ops unix_seqpacket_ops = {
 static struct proto unix_proto = {
 	.name			= "UNIX",
 	.owner			= THIS_MODULE,
+	.sockets_allocated	= &unix_nr_socks,
 	.obj_size		= sizeof(struct unix_sock),
 };