Make key export callback and context connection-specific

Fixes #2188

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/ChangeLog.d/key-export.txt b/ChangeLog.d/key-export.txt
index 5882d23..10d8c89 100644
--- a/ChangeLog.d/key-export.txt
+++ b/ChangeLog.d/key-export.txt
@@ -1,8 +1,13 @@
 API changes
-   * mbedtls_ssl_conf_export_keys_ext_cb() has been removed.
+   * mbedtls_ssl_conf_export_keys_ext_cb() and
+     mbedtls_ssl_conf_export_keys_cb() have been removed
+     and replaced by a new API
+     mbedtls_ssl_set_export_keys_cb().
    * The signature of key export callbacks configured via
-     mbedtls_ssl_conf_export_keys_cb() has changed, and raw
-     keys and IVs are no longer exported. Further, callbacks
+     mbedtls_ssl_set_export_keys_cb() is different from that
+     of the previous mbedtls_ssl_conf_export_keys_cb(): First,
+     raw keys and IVs are no longer exported. Further, callbacks
      now receive an additional parameter indicating the type
      of secret that's being exported, paving the way for the
-     larger number of secrets in TLS 1.3.
+     larger number of secrets in TLS 1.3. Finally, the key export
+     callback and context are now connection-specific.