Global parser functions to return 1 when property unchanged

Global parser functions to return 1 when property unchanged

Currently, wpa_config_set(), the function that sets wpa_supplicant
per-network properties, returns 1 when a property it attempts to set is
unchanged. Its global parallel, wpa_config_process_global(), doesn't do
this even though much of the code is very similar. Change this, and
several of the parser functions, to resemble the per-network parser and
setter functions.

Signed-off-by: Matthew Wang <matthewmwang@chromium.org>