connection-editor: Fix handling of wired 802-1x security setting

Function nm_setting_duplicate() can't copy object's data.
As a result a value of the "Ignore CA certificate" checkbox was
always lost. So don't copy settings, just use g_object_ref() again
and remove the 8021x setting from the temporary object to prevent
the clearing of secrets.

https://mail.gnome.org/archives/networkmanager-list/2016-August/msg00109.html

Fixes: c21d56dd