networking: More robust detection of masters
networking: More robust detection of masters

Sometimes when a bond has been deleted, NetworkManager keeps
ActiveConnection.Master of a previous slave pointing to the now
non-existing bond device.  We detect these spurious masters by looking
at how many slaves they have.

Closes #10303
moraleslazaro/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,garrett/cockpit,andreasn/cockpit,cockpituous/cockpit,deryni/cockpit,cockpituous/cockpit,garrett/cockpit,andreasn/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,moraleslazaro/cockpit,andreasn/cockpit,cockpituous/cockpit,andreasn/cockpit,cockpit-project/cockpit,cockpituous/cockpit,deryni/cockpit,deryni/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,deryni/cockpit,martinpitt/cockpit,garrett/cockpit,garrett/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,andreasn/cockpit,deryni/cockpit,andreasn/cockpit,andreasn/cockpit,cockpituous/cockpit,mvollmer/cockpit,garrett/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit