wifi: ath9k: avoid referencing uninit memory in ath9k_wmi_ctrl_rx

In the Linux kernel, the following vulnerability has been resolved:

wifi: ath9k: avoid referencing uninit memory in ath9k_wmi_ctrl_rx

For the reasons also described in commit b383e8abed41 ("wifi: ath9k: avoid

uninit memory read in ath9k_htc_rx_msg()"), ath9k_htc_rx_msg() should

validate pkt_len before accessing the SKB.

For example, the obtained SKB may have been badly constructed with

pkt_len = 8. In this case, the SKB can only contain a valid htc_frame_hdr

but after being processed in ath9k_htc_rx_msg() and passed to

ath9k_wmi_ctrl_rx() endpoint RX handler, it is expected to have a WMI

command header which should be located inside its data payload.

Implement sanity checking inside ath9k_wmi_ctrl_rx(). Otherwise, uninit

memory can be referenced.

Tested on Qualcomm Atheros Communications AR9271 802.11n .

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.