udp: use sk_protocol instead of pcflag to detect udplite sockets

In the udp_sock struct, the 'forward_deficit' and 'pcflag' fields
share the same cacheline. While the first is dirtied by
udp_recvmsg, the latter is read, possibly several times, by the
bottom half processing to discriminate between udp and udplite
sockets.

With this patch, sk->sk_protocol is used to check is the socket is
really an udplite one, avoiding some cache misses per
packet and improving the performance under udp_flood with
small packet up to 10%.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/udp.h

@@ -115,6 +115,6 @@ static inline bool udp_get_no_check6_rx(struct sock *sk)
 #define udp_portaddr_for_each_entry_rcu(__sk, list) \
 	hlist_for_each_entry_rcu(__sk, list, __sk_common.skc_portaddr_node)
 
-#define IS_UDPLITE(__sk) (udp_sk(__sk)->pcflag)
+#define IS_UDPLITE(__sk) (__sk->sk_protocol == IPPROTO_UDPLITE)
 
 #endif	/* _LINUX_UDP_H */