DPP: Discard DPP Action frame in AP mode if no global DPP context

DPP: Discard DPP Action frame in AP mode if no global DPP context

For AP mode in wpa_supplicant, e.g., for P2P GO interfaces, the global
DPP context does not exist support DPP functionality and this could
result in dereferencing a NULL pointer in wpa_supplicant if an
unexpected frame is received. Discard the received DPP Action frames in
such cases instead of trying to process them.

Fixes: e00f780e2bdd ("DPP2: hostapd as TCP Relay")
Signed-off-by: Jouni Malinen <quic_jouni@quicinc.com>