wifi: mt76: mt7925: validate skb length in testmode query

wifi: mt76: mt7925: validate skb length in testmode query

In mt7925_tm_query(), the response skb from mt76_mcu_send_and_get_msg()
is used in a memcpy without validating its length:

  memcpy(evt_resp, skb->data + 8, MT7925_EVT_RSP_LEN);

where MT7925_EVT_RSP_LEN is 512. If the firmware returns a response
shorter than 520 bytes (8 + 512), this reads beyond the skb data
buffer. The over-read data is then returned to userspace via nla_put()
in mt7925_testmode_dump().

Add a length check before the memcpy to ensure the skb contains
sufficient data.

Fixes: c948b5da6bbe ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Signed-off-by: Aviel Zohar <avielzohar123@gmail.com>
Link: https://patch.msgid.link/20260413033136.5417-2-avielzohar123@gmail.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>