interface: fix removal of dynamic interfaces

interface: fix removal of dynamic interfaces

Set config state to remove for dynamic interfaces in the following cases :
-interface is set as not available
-interface is set as down
-interface is set as having no link state
This will trigger an interface delete upon the next call of interface_handle_config_change

Before this change you could end up with lingering inactive dynamic
interfaces in case the aliased interface went down as before a dynamic
interface was only removed when set down via ubus

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>