mac80211: don't teardown sdata on sdata stop

Interfaces are being initialized (setup) on addition,
and torn down on removal.

However, p2p device is being torn down when stopped,
resulting in the next p2p start operation being done
on uninitialized interface.

Solve it by calling ieee80211_teardown_sdata() only
on interface removal (for the non-netdev case).

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
[squashed in fix to call teardown after unregister]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>