P2P: Indicate scan during group formation as P2P probe
The interface may not yet have been set to P2P client mode immediately
after GO Negotiation when doing the scan before association request.
Consequently, the scan request in this state has to specify that the
specific P2P probe mode is used to disable IEEE 802.11b rates.
Signed-hostap: Jouni Malinen <j@w1.fi>