nl80211: Hold wdev identification for P2P Device

nl80211: Hold wdev identification for P2P Device

Add wdev_id to i802_bss. wdev_id_set indicates whether this id is
available. Use wdev_id if assigned, instead of ifindex. Use wdev_id for
events that come from the kernel to identify the relevant interface.
This commit does not assign wdev_id value for the BSS yet, i.e., this is
only preparation for the value to be used in a future commit.

Signed-off-by: David Spinadel <david.spinadel@intel.com>