Generate Exposure Notification Service payload according A/G

[sciabarracom]

The Exposure Notification Service payload has four sections:

1. Flags Section — Bluetooth Low Energy general discoverable mode (bit 1) shall be set to 1.
2. Complete 16-bit Service UUID Section — The UUID is 0xFD6F, and shall precede the Service Data section.
3. Service Data 16-bit UUID Section — This section shall have two different sections in its payload:
   a. A 16 byte Rolling Proximity Identifier.
   b. A 4 byte Associated Encrypted Metadata that contains the following (LSB first):
   i. Byte 0 — Versioning.
   • Bits 7:6 — Major version (01).
   • Bits 5:4 — Minor version (00).
   • Bits 3:0 — Reserved for future use.
   ii. Byte 1 — Transmit power level.
   • This is the measured radiated transmit power of Bluetooth Advertisement packets, and is used to
   improve distance approximation. The range of this field shall be -127 to +127 dBm.
   iii. Byte 2 — Reserved for future use.
   iv. Byte 3 — Reserved for future use.