This patch ensures that changes in attributes of interfaces will emit
errors except if they are missing from the XML.
Previously we were falsely reporting successful updates, because some
changed attributes got overwritten before the validity checks.

https://bugzilla.redhat.com/show_bug.cgi?id=1599513Signed-off-by: NKaterina Koukiou <kkoukiou@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>