Function decodeMACHeader

IEEE Std 802.15.4-2020, 7.2.2 (MAC header fields) 05-3474-23 R23.1, Annex C.2 (Zigbee MAC frame subset)

Decode MAC header from frame. HOT PATH: Called for every incoming MAC frame.

SPEC COMPLIANCE NOTES:

• ✅ Validates addressing mode combinations and PAN ID compression per Zigbee limits
• ✅ Parses beacon, command, and data header extensions (GTS, pending list) as required
• ⚠️ Supports MAC security only for legacy 2003 mode; production security handled above MAC DEVICE SCOPE: All logical devices.