[nat64] update Mapping::ToString() to include translated ports (#11886)

When `OPENTHREAD_CONFIG_NAT64_PORT_TRANSLATION_ENABLE` is enabled,
multiple `Mapping` entries can exist for the same IPv6 and IPv4
addresses, differing only by their protocol ports.

To distinguish between these entries in logs and diagnostics, this
change updates `Mapping::ToString()` to include the source and
translated port numbers in the generated string output.

src/core/net/nat64_translator.cpp

@@ -348,7 +348,12 @@ Translator::Mapping::InfoString Translator::Mapping::ToString(void) const
 {
     InfoString string;
 
+#if OPENTHREAD_CONFIG_NAT64_PORT_TRANSLATION_ENABLE
+    string.Append("%s,%u -> %s,%u", mIp6Address.ToString().AsCString(), mSrcPortOrId,
+                  mIp4Address.ToString().AsCString(), mTranslatedPortOrId);
+#else
     string.Append("%s -> %s", mIp6Address.ToString().AsCString(), mIp4Address.ToString().AsCString());
+#endif
 
     return string;
 }

src/core/net/nat64_translator.hpp

@@ -323,7 +323,7 @@ private:
 
     struct Mapping : public InstanceLocatorInit, public LinkedListEntry<Mapping>
     {
-        static constexpr uint16_t kInfoStringSize = 70;
+        static constexpr uint16_t kInfoStringSize = 80;
 
         typedef String<kInfoStringSize> InfoString;