Update ChangeLog
Add an entry in ChangeLog describing the fix.
diff --git a/ChangeLog b/ChangeLog
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@@ -15,6 +15,8 @@
* Add explicit integer to enumeration type casts to example program
programs/pkey/gen_key which previously led to compilation failure
on some toolchains. Reported by phoenixmcallister. Fixes #2170.
+ * Run the AD too long test only if MBEDTLS_CCM_ALT is not defined.
+ Raised as a comment in #1996.
= mbed TLS 2.7.8 branch released 2018-11-30