device: fix bug when deactivating port connections asynchronously

Summary

When the attach_port()/detach_port() methods do not return immediately (currently, only for OVS ports), the following situation can arise:

• nm_device_controller_attach_port() starts the attachment uby sending the command to ovsdb. Note that here we don't set PortInfo->port_is_attached to TRUE yet; that happens only after the asynchronous command returns;

• the activation of the port gets interrupted because the connection is deleted;

• the port device enters the deactivating state, triggering function port_state_changed()

• the function calls nm_device_controller_release_port() which checks whether the port is already attached; since PortInfo->port_is_attached is not set yet, it assumes the port doesn't need to be detached;

• in the meantime, the ovsdb operation succeeds. As a consequence, the kernel link is created even if the connection no longer exists.

Fix this by turning port_is_attached into a tri-state variable that also tracks when the port is attaching. When it is, we need to perform an explicit detach during deactivation.

Fixes: 9fcbc6b3 ('device: make attach_port() asynchronous')

Resolves: https://issues.redhat.com/browse/RHEL-58026