Add some of the Device Discovery logic and the DBus API. Device
Discovery is documented as having three states: the Scan Phase, the Find
Phase and the Listen State.
This patch adds the Scan Phase and the next patch adds the Listen State,
which will happen sequentially in a loop until discovery is stopped.
The Find Phase, which is documented as happening at the beginning of the
Discovery Phase, is incorporated into the Scan Phases. The difference
between the two is that Find Phase scans all of the supported channels
while the Scan Phase only scans the three "social" channels. In
practical terms the Find Phase would discover existing groups, which may
operate on any channel, while the Scan Phase will only discover P2P
Devices -- peers that are not in a group yet. To cover existing groups,
we add a few "non-social" channels to each of our active scans
implementing the Scan Phases.
Implement the Enabled property on device interface. The P2P device is
currently disabled on startup but automatically enabling the P2P device
can be considered.
