wifi: mac80211: do not drop packets smaller than the LLC-SNAP header on fast-rx

Since STP TCN frames are only 7 bytes, the pskb_may_pull call returns an error.
Instead of dropping those packets, bump them back to the slow path for proper
processing.

Fixes: 49ddf8e6e2 ("mac80211: add fast-rx path")
Reported-by: Chad Monroe <chad.monroe@smartrg.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -4708,7 +4708,7 @@ static bool ieee80211_invoke_fast_rx(struct ieee80211_rx_data *rx,
 
 	if (!(status->rx_flags & IEEE80211_RX_AMSDU)) {
 		if (!pskb_may_pull(skb, snap_offs + sizeof(*payload)))
-			goto drop;
+			return false;
 
 		payload = (void *)(skb->data + snap_offs);