mt76x02: do not enable RTS/CTS by default

My commit 26a7b547 ("mt76x02: set protection according to ht
operation element") enabled by default RTS/CTS protection for OFDM
and CCK traffic, because MT_TX_RTS_CFG_THRESH is configured to non
0xffff by initvals and .set_rts_threshold callback is not called by
mac80211 on initialization, only on user request or during
ieee80211_reconfig() (suspend/resuem or restart_hw).

Enabling RTS/CTS cause some problems when sending probe request
frames by hcxdumptool penetration tool, but I expect it can cause
other issues on different scenarios.

Restore previous setting of RTS/CTS being disabled by default for
OFDM/CCK by changing MT_TX_RTS_CFG_THRESH initvals to 0xffff.

Fixes: 26a7b547 ("mt76x02: set protection according to ht operation element")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>