Multiple interfaces with empty identifier are marked as invalid
The NIC validation is not treating empty identifier correctly. While the validation method on host skips such interfaces, validation on NIC side tries to enforce uniqueness even of empty identifiers. This causes problems during provisioning of host with multiple interfaces, preventing the TFTP change because of interface being invalid. To reproduce, create a host with two interfaces with empty identifier. Then try editing the host, e.g. changing the comment attribute. It fails on interface identifier being already taken.
Fixes #15238 - ignore empty NIC identifiers
(cherry picked from commit 7e20cbac5951b858716268cce29f0fad16b71081)