passt: Add IPv6 and NDP support, further fixes for IPv4 CT

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

util.c

@@ -7,8 +7,11 @@
  *
  */
 
+#include <stdio.h>
 #include <stdint.h>
 #include <stddef.h>
+#include <linux/ipv6.h>
+#include <arpa/inet.h>
 
 /**
  * csum_fold() - Fold long sum for IP and TCP checksum
@@ -46,3 +49,39 @@ uint16_t csum_ip4(void *buf, size_t len)
 
 	return ~csum_fold(sum);
 }
+
+unsigned char *ipv6_l4hdr(struct ipv6hdr *ip6h, uint8_t *proto)
+{
+	int offset, len, hdrlen;
+	struct ipv6_opt_hdr *o;
+	uint8_t nh;
+
+	len = ntohs(ip6h->payload_len);
+	offset = 0;
+
+	while (offset < len) {
+		if (!offset) {
+			nh = ip6h->nexthdr;
+			hdrlen = sizeof(struct ipv6hdr);
+		} else {
+			nh = o->nexthdr;
+			hdrlen = (o->hdrlen + 1) * 8;
+		}
+
+		if (nh == 59)
+			return NULL;
+
+		if (nh == 0   || nh == 43  || nh == 44  || nh == 50  ||
+		    nh == 51  || nh == 60  || nh == 135 || nh == 139 ||
+		    nh == 140 || nh == 253 || nh == 254) {
+			offset += hdrlen;
+			o = (struct ipv6_opt_hdr *)(unsigned char *)ip6h +
+								    offset;
+		} else {
+			*proto = nh;
+			return (unsigned char *)(ip6h + 1) + offset;
+		}
+	}
+
+	return NULL;
+}