Comment 2 for bug 1293184

> If there are ports on the network belonging to different tenants that means that the network is shared, hence the check.
> I think the bug is not valid

As I explained, if a network is marked "external" then it can be set as a gateway for routers of other tenants. This creates a port for the router on the network.
If I mark this network as shared or not shared this doesn't affect these ports or the usage of the network as a gateway.

The problem is that if there are no instance ports on the network, the "shared" mark can't be removed even though it's not used by any instance.

For example, if I have a non-external network with no instance ports on it I can update it to shared and then immediately update to non-shared, this will work.
However, if I have an external network that is being used as a gateway then I can update it to shared but immediately updating to non-shared will fail because of the router port, and this is the cause of the bug.