Notification of SDP changes to device drivers

Hi all,

This patch is the one that I mentioned that was needed to HDP for 
updating the services. When a search services is performed using the
device API, the stored records will be compared with the new found and 
if there are any diferences the driver will receive a notification.

I've made this optional in order to keep backwards compatibility, so no extra
changes are needed in the drivers if they don't care about the SDP changes.

Regards