mac80211: sequence number micro-optimisation

There's no need to mask the variable with 0xFFF0
since we ever only use it as a u16 and the lowest
four bits can't ever be non-zero. The compiler
cannot infer the latter, and therefore has to emit
code to do the masking.
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/tx.c

@@ -700,7 +700,6 @@ ieee80211_tx_h_sequence(struct ieee80211_tx_data *tx)
 		/* for pure STA mode without beacons, we can do it */
 		hdr->seq_ctrl = cpu_to_le16(tx->sdata->sequence_number);
 		tx->sdata->sequence_number += 0x10;
-		tx->sdata->sequence_number &= IEEE80211_SCTL_SEQ;
 		return TX_CONTINUE;
 	}