Add the intf_entry.intf_index member.

This is the operating system's interface index, as used by
if_indextoname and sockaddr_sin6.sin6_scope_id.

libdnet-stripped/include/dnet/intf.h

@@ -19,6 +19,7 @@
 struct intf_entry {
 	u_int		intf_len;		    /* length of entry */
 	char		intf_name[INTF_NAME_LEN];   /* interface name */
+	u_int		intf_index;		    /* interface index (r/o) */
 	u_short		intf_type;		    /* interface type (r/o) */
 	u_short		intf_flags;		    /* interface flags */
 	u_int		intf_mtu;		    /* interface MTU */

libdnet-stripped/src/intf.c

@@ -391,6 +391,11 @@ _intf_get_noalias(intf_t *intf, struct intf_entry *entry)
 
 	strlcpy(ifr.ifr_name, entry->intf_name, sizeof(ifr.ifr_name));
 	
+	/* Get interface index. */
+	if (ioctl(intf->fd, SIOCGIFINDEX, &ifr) < 0)
+		return (-1);
+	entry->intf_index = ifr.ifr_ifindex;
+
 	/* Get interface flags. */
 	if (ioctl(intf->fd, SIOCGIFFLAGS, &ifr) < 0)
 		return (-1);