r92su: cfg80211_rx_mgmt api change

The api for cfg80211_rx_mgmt has changed with:

  commit 19504cf5f35fbe85db811fce9f4392a0cbdada2f
  Author: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
  Date:   Thu Aug 15 14:51:28 2013 +0300

    cfg80211: add flags to cfg80211_rx_mgmt()

Since cfg80211_rx_mgmt isn't working anyway, let's just disable
the call.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>