Fix logic when pushed cipher triggers tun reopen and ignore more options

Fix logic when pushed cipher triggers tun reopen and ignore more options

The logic was inverted. Only when link-mtu is used, pushing a cipher can
change the MTU and not the other way round. (found by zeropath)

Also ignore a few more options that should not trigger a reopen of tun
in push message.

Reported-by: Joshua Rogers <contact@joshua.hu>
Found-by: ZeroPath (https://zeropath.com/)
Change-Id: I76eb584024610a6054a069340adbac988abf686c
Signed-off-by: Arne Schwabe <arne-openvpn@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1321
Message-Id: <20251029065316.10182-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg33989.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>