ipv6: remove useless spin_lock/spin_unlock

xchg is atomic, so there is no necessary to use spin_lock/spin_unlock
to protect it. At last, remove the redundant
opt = xchg(&inet6_sk(sk)->opt, opt); statement.

Signed-off-by: Duan Jiong <duanj.fnst@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ipv6_sockglue.c

@@ -110,12 +110,8 @@ struct ipv6_txoptions *ipv6_update_options(struct sock *sk,
 			icsk->icsk_ext_hdr_len = opt->opt_flen + opt->opt_nflen;
 			icsk->icsk_sync_mss(sk, icsk->icsk_pmtu_cookie);
 		}
-		opt = xchg(&inet6_sk(sk)->opt, opt);
-	} else {
-		spin_lock(&sk->sk_dst_lock);
-		opt = xchg(&inet6_sk(sk)->opt, opt);
-		spin_unlock(&sk->sk_dst_lock);
 	}
+	opt = xchg(&inet6_sk(sk)->opt, opt);
 	sk_dst_reset(sk);
 
 	return opt;