hostapd: Compile time option for Config Knobs feature

The Config Knob feature is kept under compile time
flag "CONFIG_STA_POLICY", which is Enabled by default.

BUG=b:79511734
TEST=Sanity test on hostapd
    - Verified the compilation
    - Verified that following commands are not supported if Config knobs is disabled
      sta_policy_add
      sta_policy_del
      sta_policy_get
    - Verified that Config knobs works as it is if Enabled
CQ-DEPEND=CL:*624207

Change-Id: Ic404fc3bfaa9e54e405bf7c72d9c6e46627d4928
Reviewed-on: https://chromium-review.googlesource.com/1044385
Commit-Ready: Dheeraj KM <dheeraj.km@globaledgesoft.com>
Tested-by: Dheeraj KM <dheeraj.km@globaledgesoft.com>
Reviewed-by: Srinivasa duvvuri <sduvvuri@google.com>
9 files changed