Fix DKIM signature when disclaimer is added

[DavidePrincipi]

This PR proposal disables the submission DKIM milter when the optional disclaimer package is installed, and reverts the fix of NethServer/dev#5514

The DKIM signature issue seems due to our Postfix configuration which double signs outbound messages:

1. the first time with submission_smtpd_milters (used by SMTP port 587)
2. the second time with non_smtpd_milters (used by sendmail)

[root@vm8 ~]# postconf -n | grep smtpd_milt
non_smtpd_milters = unix:/var/run/opendkim/milter
smtpd_milters = unix:/var/run/rspamd/worker-proxy
submission_smtpd_milters = unix:/var/run/rspamd/worker-proxy, unix:/var/run/opendkim/milter

NethServer/dev#5528

[stephdl]

Authentication-Results: mx.google.com;
       dkim=neutral (body hash did not verify) header.i=@de-labrusse.fr header.s=default header.b=SG3PqP53;

Sorry but with your change gmail doesn't accept the dkim

# postconf -n | grep smtpd_milt
non_smtpd_milters = unix:/var/run/opendkim/milter
smtpd_milters = unix:/var/run/rspamd/worker-proxy
submission_smtpd_milters = unix:/var/run/rspamd/worker-proxy

[DavidePrincipi]

Can you "gist" the full message (both headers+body?)

[nethbot]

in 7.5.1804/autobuild:

• nethserver-mail2-common-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm
• nethserver-mail2-disclaimer-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm
• nethserver-mail2-filter-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm
• nethserver-mail2-getmail-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm
• nethserver-mail2-ipaccess-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm
• nethserver-mail2-p3scan-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm
• nethserver-mail2-server-2.2.1-1.3.pr51.gef71036.ns7.noarch.rpm

[stephdl]

@davidep https://gist.github.com/stephdl/ef6947d3aae31631c3787d09da5fa10e