Merge #19797: net: Remove old check for 3-byte shifted IP addresses from pre-0.2.9 nodes

7b6d0f10a7 Remove old check for 3-byte shifted IP addresses from pre-0.2.9 node messages (Raúl Martínez (RME))

Pull request description:

  The change removes an old check for IPv6 addresses in range ::ff:ff00:0:0:0/72 that were created due to a bug in size field of addr messages for 0.2.8 nodes and before.

  This check is no longer needed as they are no more pre 0.2.9 nodes on the network (as per bitnodes network snapshot).

  Credits for discovering this go to sipa in https://github.com/bitcoin/bitcoin/pull/19628#discussion_r475907453

  Thanks for the attention!

ACKs for top commit:
  sipa:
    utACK 7b6d0f10a7
  vasild:
    ACK 7b6d0f1

Tree-SHA512: c5fab59dda2acafe143f607a4c5b636a54ac76fba651cad1ad1b09c94e88ab39503a31c2244c8f2664da68456c2a870c601d8894139c55cde9ece8161913ed2e

src/netaddress.cpp

@@ -270,17 +270,6 @@ bool CNetAddr::IsLocal() const
  */
 bool CNetAddr::IsValid() const
 {
-    // Cleanup 3-byte shifted addresses caused by garbage in size field
-    // of addr messages from versions before 0.2.9 checksum.
-    // Two consecutive addr messages look like this:
-    // header20 vectorlen3 addr26 addr26 addr26 header20 vectorlen3 addr26 addr26 addr26...
-    // so if the first length field is garbled, it reads the second batch
-    // of addr misaligned by 3 bytes.
-    if (IsIPv6() && memcmp(m_addr.data(), IPV4_IN_IPV6_PREFIX.data() + 3,
-                           sizeof(IPV4_IN_IPV6_PREFIX) - 3) == 0) {
-        return false;
-    }
-
     // unspecified IPv6 address (::/128)
     unsigned char ipNone6[16] = {};
     if (IsIPv6() && memcmp(m_addr.data(), ipNone6, sizeof(ipNone6)) == 0) {