Make clicks on io menu bundles always connect

Make clicks on io menu bundles always connect

If a bundle was already connected, a click on the corresponding entry
disconnected it, essentially giving toggle semantics to the io menus.
This behavior has three problems:

 — When clicking on a not yet connected bundle, the new bundle replaces
   any already connected one. This is not consistent with a toggle mode.
 — It is a less discoverable and less easy way to disconnect a bundle
   than the already present "Disconnect" menu entry.
 — Bundles that match the I/O channels only partially (recently added to cater
   for e.g. MIDI+STEREO tracks connecting to Master) are never
   considered "connected" because the channels are not connected 1:1.
   Those will thus never toggle, making the behavior inconsistent.

Change the semantics to ensure a bundle is connected on click instead.