Function encodeZigbeeNWKFrame

05-3474-23 R23.1, Table 3-20 (NWK data frame format) & Annex A (NWK security)

SPEC COMPLIANCE NOTES:

• ✅ Constructs NWK frame then encrypts/authenticates payload per Zigbee security flag
• ✅ Copies authentication tag trailing bytes as mandated by CCM*
• ⚠️ Caller must ensure payload length respects NWK/APS combined MTU when security enabled DEVICE SCOPE: All logical devices