This patch changes the behavior of the headset=auto switch for module-bluez5-discover.
With headset=auto now both backends will be active at the same time for the AG role and
the switching between the backends is only done for the HS role.
headset=ofono and headset=native remain unchanged.

This allows to use old HSP only headsets while running ofono and to have headset support
via pulseaudio if ofono is started with the --noplugin=hfp_ag_bluez5 option.