mt76: mt7615: reduce VHT maximum MPDU length

With a maximum length of 7991, the radio sometimes locks up under load when
transmitting A-MSDU frames to lots of stations. Using the lower limit makes
it work reliably again

Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7615/init.c

@@ -500,7 +500,6 @@ void mt7615_init_device(struct mt7615_dev *dev)
 	dev->mphy.sband_2g.sband.ht_cap.cap |= IEEE80211_HT_CAP_LDPC_CODING;
 	dev->mphy.sband_5g.sband.ht_cap.cap |= IEEE80211_HT_CAP_LDPC_CODING;
 	dev->mphy.sband_5g.sband.vht_cap.cap |=
-			IEEE80211_VHT_CAP_MAX_MPDU_LENGTH_7991 |
 			IEEE80211_VHT_CAP_MAX_A_MPDU_LENGTH_EXPONENT_MASK;
 	mt7615_cap_dbdc_disable(dev);
 	dev->phy.dfs_state = -1;