cfg80211: fix sending WoWLAN TCP wakeup settings

The code sending the current WoWLAN TCP wakeup settings in
nl80211_send_wowlan_tcp() is not closing the nested attribute,
thus causing the parser to get confused on the receiver side
in userspace (iw). Fix this.

Cc: stable@vger.kernel.org [3.9]
Reported-by: Deepak Arora <deepakx.arora@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>