Dovecot: Fix for logjam attack

roles/mailserver/files/etc_dovecot_conf.d_10-ssl.conf

@@ -48,3 +48,6 @@ ssl_protocols = !SSLv2 !SSLv3
 
 # SSL crypto device to use, for valid values run "openssl engine"
 #ssl_crypto_device =
+
+# DH parameters length to use.
+ssl_dh_parameters_length = 2048