use preinstalled dh params file instead of generating a new one which takes a lot of time

Signed-off-by: Michael Kaufmann <d00p@froxlor.org>

lib/configfiles/bullseye.xml

@@ -3500,7 +3500,7 @@ ssl_client_ca_dir = /etc/ssl/certs
 # Generate new params with `openssl dhparam -out /etc/dovecot/dh.pem 4096`
 # Or migrate from old ssl-parameters.dat file with the command dovecot
 # gives on startup when ssl_dh is unset.
-ssl_dh = </etc/dovecot/dh.pem
+ssl_dh = </usr/share/dovecot/dh.pem
 
 # Minimum SSL protocol version to use. Potentially recognized values are SSLv3,
 # TLSv1, TLSv1.1, and TLSv1.2, depending on the OpenSSL version used.
@@ -4115,7 +4115,6 @@ plugin {
 						</file>
 					</files>
 					<commands index="1">
-						<command><![CDATA[openssl dhparam -out /etc/dovecot/dh.pem 4096]]></command>
 						<command><![CDATA[service dovecot restart]]></command>
 					</commands>
 				</general>