Use additional interface for the WiFi Aware Discovery operations.

NAN operations are currently done on the STA interface.This resulted
in the NAN sessions getting terminated in all the instances where the
STA interface is restarted (IFF DOWN/UP), due to connected MAC
randomization.
Hence, remove the dependency of NAN over STA interface. This change
expects the driver to create a dedicated interface for the
NAN operations. The iface name needs to be set in "wifi.aware.interface"
property.

Bug: 1636219
Test: HAL unit tests
Test: Device boots up and connects to wifi network.
Change-Id: I1b6d64eb94334172a8cd621d0b15ed8c8dc87f91