Support translating ICMP errors.

When receiving ICMPv6 messages from IPv6-only nodes, use
255.0.0.<ttl> as a fake IPv4 source address. It's better than
nothing.

Bug: 8276725
Change-Id: Iae93f75764cb9cd875af9bb5f1862a0dce2c2fa7
diff --git a/translate.h b/translate.h
index 120fecf..fded251 100644
--- a/translate.h
+++ b/translate.h
@@ -27,6 +27,7 @@
 // specific parts of the packet. The packet_* functions operate on all the packet segments past a
 // given position.
 enum clat_packet_index { CLAT_POS_TUNHDR, CLAT_POS_IPHDR, CLAT_POS_TRANSPORTHDR,
+                         CLAT_POS_ICMPERR_IPHDR, CLAT_POS_ICMPERR_TRANSPORTHDR,
                          CLAT_POS_PAYLOAD, CLAT_POS_MAX };
 typedef struct iovec clat_packet[CLAT_POS_MAX];