Random zyd(4) fixes to bring TX handling in line with rsu, etc

• don't free buffers in the TX routine, only in transmit/raw_xmit
• free nodes + references
• .. and free those nodes/references /before/ net80211 detach

Tested:

• STA mode: zyd0: HMAC ZD1211B, FW 47.25, RF AL2230 S0, PA0 LED 0 BE0 NP1 Gain1 F0