ipv6: icmp: use this_cpu_read() in icmpv6_sk()

In general, this_cpu_read(*X) is faster than *this_cpu_ptr(X)

Also remove the inline attibute, totally useless.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/icmp.c

@@ -79,9 +79,9 @@
  *
  *	On SMP we have one ICMP socket per-cpu.
  */
-static inline struct sock *icmpv6_sk(struct net *net)
+static struct sock *icmpv6_sk(struct net *net)
 {
-	return *this_cpu_ptr(net->ipv6.icmp_sk);
+	return this_cpu_read(*net->ipv6.icmp_sk);
 }
 
 static int icmpv6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,