wificond: Generic API to send 802.11 management frames

Implement interfacing with nl80211 to send arbitrary 802.11 management
frames, and notify the caller via callback when the transmitted frame
has been ACKed.

Bug: 112029045
Test: Manually triggered transmissions of 802.11 Probe Request frames,
and confirmed that ACKs were received.
Test: system/connectivity/wificond/runtests.sh
Change-Id: I843b98f5e26e0263c632be47cf29920c0f426944
15 files changed