Enforce dhm_min_bitlen exactly, not just the byte size

In a TLS client, enforce the Diffie-Hellman minimum parameter size
set with mbedtls_ssl_conf_dhm_min_bitlen() precisely. Before, the
minimum size was rounded down to the nearest multiple of 8.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/ChangeLog.d/dhm_min_bitlen.txt b/ChangeLog.d/dhm_min_bitlen.txt
new file mode 100644
index 0000000..e7ea827
--- /dev/null
+++ b/ChangeLog.d/dhm_min_bitlen.txt
@@ -0,0 +1,4 @@
+Bugfix
+   * In a TLS client, enforce the Diffie-Hellman minimum parameter size
+     set with mbedtls_ssl_conf_dhm_min_bitlen() precisely. Before, the
+     minimum size was rounded down to the nearest multiple of 8.