tests: Change wpas_config_file test for dedicated P2P Device case

SAVE_CONFIG command on the global control interface tries to save
the config file on all interfaces. The test disabled updating the
config file only on one interface, thus for configurations that
support a dedicated P2P Device interface, saving the config file
would still have succeeded on the P2P Device interface.

Fix the test by disabling updating the configuration file on the global
control interface (which will, in practice, disable this for the P2P
Device interface) in addition to disabling it on the main interface.

Signed-off-by: Avraham Stern <avraham.stern@intel.com>