hostapd: extend DPP ucode API with WPS M7/M8 encrypted settings handling

hostapd: extend DPP ucode API with WPS M7/M8 encrypted settings handling

Add callbacks to intercept WPS M7 reception (registrar side) and M8
reception (enrollee side), allowing external code to inject extra
encrypted attributes and optionally skip credential building.

On the registrar side, the m7_rx callback receives the decrypted M7
content and can return extra data to include in M8's encrypted settings
as well as a flag to skip credential generation.

On the enrollee side, add a wps_set_m7 method to set extra encrypted
data for M7, and a m8_rx callback to handle the decrypted M8 content
externally.

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