Function decodeMACPayload

IEEE Std 802.15.4-2020, 7.2.2.4 (MAC payload and FCS handling) 05-3474-23 R23.1, Annex C.2 (Zigbee MAC frame subset)

SPEC COMPLIANCE NOTES:

• ✅ Rejects MAC-layer security frames in line with Zigbee host design (security handled at NWK/APS)
• ✅ Verifies FCS presence and stores it for diagnostics per Zigbee stack requirements
• ⚠️ Leaves MIC validation to upper layers because MAC security is disabled DEVICE SCOPE: All logical devices.