To enhance privacy, generate a random device address for P2P interface.
If there is no saved persistent group, it generate a new random MAC
address on bringing up p2p0. If there is saved persistent group, it will
use last MAC address to avoid breaking group reinvoke behavior.
There are two configurations are introduced:
* p2p_device_random_mac_addr
enable device random MAC address feature, default disable.
* p2p_device_persistent_mac_addr
store last used random MAC address.
Signed-off-by: Jimmy Chen <jimmycmchen@google.com>