SoftapController: support for Fast Session Transfer

Start FST Manager before starting hostapd.
Stop FST Manager after stopping hostapd.
start/stop FST Manager is done using "netd.fstman.start" (instead
of using "ctl.start" mechanism). This is required for reducing
sepolicy rules for netd.

When FST is enabled, hostapd is started with global
control interface.

FST Soft AP support is enabled with persist.fst.softap.en system property.
persist.fst.rate.upgrade.en still controls the FST feature as a whole
and must be enabled as a prerequisite.

Change-Id: Ib552de30c7c200f46f08b72c819dba160bce8eba