hostapd: add DPP ucode API for external frame handling

hostapd: add DPP ucode API for external frame handling

Add a ucode API to hostapd and wpa_supplicant for external DPP frame
handling. This allows an external controller to intercept DPP frames
and handle the DPP protocol externally.

The API provides:
- RX callbacks (dpp_rx_action, dpp_rx_gas) called when DPP frames are
  received, allowing external handling before internal processing
- TX methods (dpp_send_action, dpp_send_gas_resp/dpp_send_gas_req) for
  transmitting DPP frames
- A ubus channel-based API (dpp_channel) for bidirectional communication
  with exclusive hook registration per interface
- CCE control for hostapd (set_cce method)

The wpa_supplicant API mirrors hostapd but adapted for STA role:
- Uses tx_gas_req instead of tx_gas_resp
- GAS RX provides full frame instead of parsed query
- No CCE control (AP-only feature)

Both implementations include:
- Timeout handling with automatic channel disconnect after 3 failures
- Hook cleanup on interface removal
- Last-caller-wins semantics for hook registration

Signed-off-by: Felix Fietkau <nbd@nbd.name>