esp4: Reorganize esp_output

We need a fallback for ESP at layer 2, so split esp_output
into generic functions that can be used at layer 3 and layer 2
and use them in esp_output. We also add esp_xmit which is
used for the layer 2 fallback.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Author: klassert

include/net/esp.h

@@ -10,4 +10,20 @@ static inline struct ip_esp_hdr *ip_esp_hdr(const struct sk_buff *skb)
 	return (struct ip_esp_hdr *)skb_transport_header(skb);
 }
 
+struct esp_info {
+	struct	ip_esp_hdr *esph;
+	__be64	seqno;
+	int	tfclen;
+	int	tailen;
+	int	plen;
+	int	clen;
+	int 	len;
+	int 	nfrags;
+	__u8	proto;
+	bool	inplace;
+};
+
+int esp_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp);
+int esp_output_tail(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp);
+int esp_input_done2(struct sk_buff *skb, int err);
 #endif