wifi: mac80211: reject TDLS operations when station is not associated

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

wifi: mac80211: reject TDLS operations when station is not associated

syzbot triggered a WARN in ieee80211_tdls_oper() by sending NL80211_TDLS_ENABLE_LINK immediately after NL80211_CMD_CONNECT, before association completed and without prior TDLS setup.

This left internal state like sdata->u.mgd.tdls_peer uninitialized, leading to a WARN_ON() in code paths that assumed it was valid.

Reject the operation early if not in station mode or not associated.