wifi-scripts: add DPP encryption support

wifi-scripts: add DPP encryption support

Add support for DPP (Device Provisioning Protocol) as both a primary
encryption type and as an optional addition to existing authentication.

Primary DPP mode (encryption=dpp):
- Sets WPA2 with key_mgmt=DPP
- Requires Management Frame Protection (ieee80211w=2)
- Supports dpp_connector, dpp_csign, dpp_netaccesskey options

Optional DPP mode (dpp=1 boolean on AP):
- Adds DPP to existing key management methods
- Allows AP to accept both DPP and other auth types
- Supports the same connector options

Both ucode and legacy shell implementations are updated for AP and STA
modes.

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