[NETFILTER]: nf_conntrack_expect: use RCU for expectation hash

Use RCU for expectation hash. This doesn't buy much for conntrack
runtime performance, but allows to reduce the use of nf_conntrack_lock
for /proc and nf_netlink_conntrack.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netfilter/nf_conntrack_expect.h

@@ -49,6 +49,8 @@ struct nf_conntrack_expect
 	/* Direction relative to the master connection. */
 	enum ip_conntrack_dir dir;
 #endif
+
+	struct rcu_head rcu;
 };
 
 #define NF_CT_EXPECT_PERMANENT 0x1