mac80211_hwsim: Timer should be initialized before device registered

mac80211_hwsim: Timer should be initialized before device registered

Otherwise if network manager starts configuring Wi-Fi interface
immidiatelly after getting notification of its creation, we will get
NULL pointer dereference:

  BUG: unable to handle kernel NULL pointer dereference at           (null)
  IP: [<ffffffff95ae94c8>] hrtimer_active+0x28/0x50
  ...
  Call Trace:
   [<ffffffff95ae9997>] ? hrtimer_try_to_cancel+0x27/0x110
   [<ffffffff95ae9a95>] ? hrtimer_cancel+0x15/0x20
   [<ffffffffc0803bf0>] ? mac80211_hwsim_config+0x140/0x1c0 [mac80211_hwsim]

Cc: stable@vger.kernel.org
Signed-off-by: Vasyl Vavrychuk <vasyl.vavrychuk@globallogic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>