Draft: [lt/team-dbus] Try switching NMDeviceTeam to async D-Bus

NMDeviceTeam uses asynchronous libteamdctl to talk to teamd.

This branch aims to do try to do that.

It also drops the usock transport support (which might be just fine).

The remaining part is the readout of port configuration on master_update_slave_connection(). I guess we could read it when we first learn it's been attached in attach_port(configure=FALSE), which is asynchronous, cache it, and use it in master_update_slave_connection(). The problem that might need fixing is that the manager first calls master_update_slave_connection() first.