nl80211: use new genl helpers for WDS

Bill Jordan's patch to allow setting the WDS
peer crossed with my patch removing all the
boilerplate code in nl80211, and consequently
he didn't make use of it yet. Fix that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>