wifi: free SKBTX_WIFI_STATUS skb tx_flags flag

wifi: free SKBTX_WIFI_STATUS skb tx_flags flag

Jason mentioned at netdevconf that we've run out of tx_flags in
the skb_shinfo(). Gain one bit back by removing the wifi bit.

We can do that because the only userspace application for it
(hostapd) doesn't change the setting on the socket, it just
uses different sockets, and normally doesn't even use this any
more, sending the frames over nl80211 instead.

Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Link: https://patch.msgid.link/20250313134942.52ff54a140ec.If390bbdc46904cf451256ba989d7a056c457af6e@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>