sctp: Replace use of sockets_allocated with specified macro.

The patch(180d8cd942ce) replaces all uses of struct sock fields'
memory_pressure, memory_allocated, sockets_allocated, and sysctl_mem
to accessor macros. But the sockets_allocated field of sctp sock is
not replaced at all. Then replace it now for unifying the code.

Fixes: 180d8cd942ce ("foundations of per-cgroup memory pressure controlling.")
Cc: Glauber Costa <glommer@parallels.com>
Signed-off-by: Tonghao Zhang <zhangtonghao@didichuxing.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/socket.c

@@ -4498,7 +4498,7 @@ static int sctp_init_sock(struct sock *sk)
 	SCTP_DBG_OBJCNT_INC(sock);
 
 	local_bh_disable();
-	percpu_counter_inc(&sctp_sockets_allocated);
+	sk_sockets_allocated_inc(sk);
 	sock_prot_inuse_add(net, sk->sk_prot, 1);
 
 	/* Nothing can fail after this block, otherwise
@@ -4542,7 +4542,7 @@ static void sctp_destroy_sock(struct sock *sk)
 	}
 	sctp_endpoint_free(sp->ep);
 	local_bh_disable();
-	percpu_counter_dec(&sctp_sockets_allocated);
+	sk_sockets_allocated_dec(sk);
 	sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 	local_bh_enable();
 }