tests: Force diff chan in p2ps_channel_active_go_and_station_different_mcc

tests: Force diff chan in p2ps_channel_active_go_and_station_different_mcc

This test case was failing pretty frequently due to an issue in being
able to send out the Provision Discovery Response frame on the operating
channel. Now that wpa_supplicant has a fix for that issue, modify this
test case to hit this error condition every time. In addition, make sure
the possible exception from p2ps_exact_seek() does not get hidden with a
failing remove_group() call in the finally section.

Signed-off-by: Jouni Malinen <j@w1.fi>