ESP: Export esp_output_fill_trailer function

The esp fill trailer method is identical for both
IPv6 and IPv4.

Share the implementation for esp6 and esp to avoid
code duplication in addition it could be also used
at various drivers code.

Signed-off-by: Raed Salem <[e-mail]>
Reviewed-by: Boris Pismenny <[e-mail]>
Reviewed-by: Saeed Mahameed <[e-mail]>
Signed-off-by: Steffen Klassert <[e-mail]>

include/net/esp.h

···
 	return (struct ip_esp_hdr *)skb_transport_header(skb);
 }
 
+static inline void esp_output_fill_trailer(u8 *tail, int tfclen, int plen, __u8 proto)
+{
+	/* Fill padding... */
+	if (tfclen) {
+		memset(tail, 0, tfclen);
+		tail += tfclen;
+	}
+	do {
+		int i;
+		for (i = 0; i < plen - 2; i++)
+			tail[i] = i + 1;
+	} while (0);
+	tail[plen - 2] = plen - 2;
+	tail[plen - 1] = proto;
+}
+
 struct esp_info {
 	struct	ip_esp_hdr *esph;
 	__be64	seqno;

net/ipv4/esp4.c

···
 	esp_output_done(base, err);
 }
 
-static void esp_output_fill_trailer(u8 *tail, int tfclen, int plen, __u8 proto)
-{
-	/* Fill padding... */
-	if (tfclen) {
-		memset(tail, 0, tfclen);
-		tail += tfclen;
-	}
-	do {
-		int i;
-		for (i = 0; i < plen - 2; i++)
-			tail[i] = i + 1;
-	} while (0);
-	tail[plen - 2] = plen - 2;
-	tail[plen - 1] = proto;
-}
-
 static struct ip_esp_hdr *esp_output_udp_encap(struct sk_buff *skb,
 					       int encap_type,
 					       struct esp_info *esp,

net/ipv6/esp6.c

···
 	esp_output_done(base, err);
 }
 
-static void esp_output_fill_trailer(u8 *tail, int tfclen, int plen, __u8 proto)
-{
-	/* Fill padding... */
-	if (tfclen) {
-		memset(tail, 0, tfclen);
-		tail += tfclen;
-	}
-	do {
-		int i;
-		for (i = 0; i < plen - 2; i++)
-			tail[i] = i + 1;
-	} while (0);
-	tail[plen - 2] = plen - 2;
-	tail[plen - 1] = proto;
-}
-
 int esp6_output_head(struct xfrm_state *x, struct sk_buff *skb, struct esp_info *esp)
 {
 	u8 *tail;