P2P: Use the first pref_chan entry as operating channel preference

P2P: Use the first pref_chan entry as operating channel preference

If there are no higher priority preference for the operating channel,
use the first pref_chan entry as the operating channel preference over
the pre-configured channel which is not really a good indication of
preference. This changes the behavior for GO Negotiation Request frame
operating channel preference value in cases where p2p_pref_chan list is
set.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>