net: add __rcu annotations to protocol

Add __rcu annotations to :
        struct net_protocol *inet_protos
        struct net_protocol *inet6_protos

And use appropriate casts to reduce sparse warnings if
CONFIG_SPARSE_RCU_POINTER=y

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/protocol.h b/include/net/protocol.h
index f1effdd3c..dc07495 100644
--- a/include/net/protocol.h
+++ b/include/net/protocol.h
@@ -89,10 +89,10 @@
 #define INET_PROTOSW_PERMANENT 0x02  /* Permanent protocols are unremovable. */
 #define INET_PROTOSW_ICSK      0x04  /* Is this an inet_connection_sock? */
 
-extern const struct net_protocol *inet_protos[MAX_INET_PROTOS];
+extern const struct net_protocol __rcu *inet_protos[MAX_INET_PROTOS];
 
 #if defined(CONFIG_IPV6) || defined (CONFIG_IPV6_MODULE)
-extern const struct inet6_protocol *inet6_protos[MAX_INET_PROTOS];
+extern const struct inet6_protocol __rcu *inet6_protos[MAX_INET_PROTOS];
 #endif
 
 extern int	inet_add_protocol(const struct net_protocol *prot, unsigned char num);