wifi: mac80211: remove band from TX info in MLO

If the interface is an MLD, then we don't know which band
the frame will be transmitted on, and we don't know how to
look up the band. Set the band information to zero in that
case, the driver cannot rely on it anyway.

No longer inline ieee80211_tx_skb_tid() since it's even
bigger now.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>