wifi: mt76: prevent non-offchannel mgmt tx during scan/roc

Only put probe request packets in the offchannel queue if
IEEE80211_TX_CTRL_DONT_USE_RATE_MASK is set and IEEE80211_TX_CTL_TX_OFFCHAN
is unset.

Fixes: 0b3be9d1 ("wifi: mt76: add separate tx scheduling queue for off-channel tx")
Reported-by: Chad Monroe <chad.monroe@adtran.com>
Link: https://patch.msgid.link/20250813121106.81559-2-nbd@nbd.name


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