mwifiex: MAC randomization should not be persistent

nl80211 provides the NL80211_SCAN_FLAG_RANDOM_ADDR for every scan
request that should be randomized; the absence of such a flag means we
should not randomize. However, mwifiex was stashing the latest
randomization request and *always* using it for future scans, even those
that didn't set the flag.

Let's zero out the randomization info whenever we get a scan request
without NL80211_SCAN_FLAG_RANDOM_ADDR. I'd prefer to remove
priv->random_mac entirely (and plumb the randomization MAC properly
through the call sequence), but the spaghetti is a little difficult to
unravel here for me.

Fixes: c2a8f0ff ("mwifiex: support random MAC address for scanning")
Cc: <stable@vger.kernel.org> # 4.9+
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>