mac80211: don't use napi_gro_receive() outside NAPI context

No matter how the driver manages its NAPI context, there's no way
sending frames to it from a timer can be correct, since it would
corrupt the internal GRO lists.

To avoid that, always use the non-NAPI path when releasing frames
from the timer.

Cc: stable@vger.kernel.org
Reported-by: Jean Trivelly <jean.trivelly@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>