Fix DNS options duplication on PUSH_UPDATE

Fix DNS options duplication on PUSH_UPDATE

Commit

    2dfc4f ("dns: deal with --dhcp-options when --dns is active")

has removed reset of tuntap DNS options. Due to that, incoming --dns
options are added to existing ones instead of overwriting them.

It has also added a new storage for --dhcp-option. The push-update
code didn't clear it and as a result, incoming --dhcp-option options
were added to existing ones instead of overwriting them.

Fixed by:

 - resetting tuntap DNS options (regression from abovementioned commit)
 - clearing dhcp options storage in push-update code

GitHub: fixes OpenVPN/openvpn#804

Change-Id: Ife4d8fc5f8e2183e61226d66a76bbaa02c06f787
Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Heiko Hund <heiko@openvpn.net>
Message-Id: <20250731122410.12200-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32448.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>