nfp: add helper to get flower cmsg length

Add a helper function that returns the length of the cmsg data when given
the cmsg skb

Signed-off-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/flower/cmsg.h

@@ -323,6 +323,11 @@ static inline void *nfp_flower_cmsg_get_data(struct sk_buff *skb)
 	return (unsigned char *)skb->data + NFP_FLOWER_CMSG_HLEN;
 }
 
+static inline int nfp_flower_cmsg_get_data_len(struct sk_buff *skb)
+{
+	return skb->len - NFP_FLOWER_CMSG_HLEN;
+}
+
 struct sk_buff *
 nfp_flower_cmsg_mac_repr_start(struct nfp_app *app, unsigned int num_ports);
 void

drivers/net/ethernet/netronome/nfp/flower/metadata.c

@@ -140,7 +140,7 @@ exit_rcu_unlock:
 
 void nfp_flower_rx_flow_stats(struct nfp_app *app, struct sk_buff *skb)
 {
-	unsigned int msg_len = skb->len - NFP_FLOWER_CMSG_HLEN;
+	unsigned int msg_len = nfp_flower_cmsg_get_data_len(skb);
 	struct nfp_fl_stats_frame *stats_frame;
 	unsigned char *msg;
 	int i;