Description of change
It is possible for bond/bridge network set-ups to have different link-layer devices with the same address and provider ID.
Previously, provider ID uniqueness was enforced across the set of devices being added, which returned errors in this scenario.
This patch allows multiple devices to be added, enforcing that the address/provider ID pairs are unique instead of provider ID being unique across the devices.
Various comments, formatting and error message enhancements are included, as well as a reduction in unnecessary machine life checking during DB transactions.
QA steps
TBC
Documentation changes
None.
Bug reference
https://bugs.launchpad.net/juju/+bug/1805966
该提问来源于开源项目：juju/juju
