nl80211: fix interface address assignment

nl80211: fix interface address assignment

When a new interface is created and already has a separate MAC address
assigned by the kernel, then we need to use that address, not just when
we've created a locally administered address.

This fixes use_p2p_group_interface=1 for iwlagn as it already makes
mac80211 assign an address for a second interface since the hardware has
two addresses assigned.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>