Clean up: Replace standard lib methods with os.h ones

Clean up: Replace standard lib methods with os.h ones

Some of the standard lib functions being used directly are redefined in
src/utils/os.h thus providing an abstraction. Change code to use os_*
functions instead of directly using the lib functions.

Signed-hostap: Nirav Shah <nirav.j2.shah@intel.com>
Signed-hostap: Angie Chinchilla <angie.v.chinchilla@intel.com>