Add init fragment for hostapd on Android

Add init fragment for hostapd on Android

This fragment defines how the Android init system should start hostapd
as a standalone service. Previously, hostapd was fork/exec'd from
Android's netd. This left hostapd with some dangling file descriptors
and a process parent minimally interested in acting as init for child
processes.

Signed-off-by: Christopher Wiley <wiley@google.com>