mac80211: Set CAN_REPLACE_PTK0 for SW crypto only drivers

Mac80211 SW crypto handles replacing PTK keys correctly.

Don't trigger needless warnings or workarounds when the driver can only
use the known good SW crypto provided by mac80211.

Signed-off-by: Alexander Wetzel <alexander@wetzel-home.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>