P2PS: Cleanup pending_p2ps_group flag

P2PS: Cleanup pending_p2ps_group flag

pending_p2ps_group flag is not always cleaned, which may later result
in an unexpected GO bring up, after PD response is transmitted in
wpas_prov_disc_resp_cb().
This can be seen when running the following hwsim tests together:
 - p2ps_channel_sta_connected_disallow_freq_mcc
 - p2ps_channel_active_go_and_station_different_mcc
Fix this by clearing pending_p2ps_group flag also when processing new
PD requests. In addition, set this flag only when really needed.

Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>