code: function extractIdentifier(packet) {
    let header = packet.substr(0,4);
    let advertiserAddress = packet.substr(14,2) +
                            packet.substr(12,2) +
                            packet.substr(10,2) +
                            packet.substr(8,2) +
                            packet.substr(6,2) +
                            packet.substr(4,2);
    let identifierType = identifiers.TYPE_EUI48;
    let txAddFlag = ((parseInt(header,16) & 0x4000) === 0x4000);
  
    if(txAddFlag) { // Advertiser address is random rather than public
      identifierType = identifiers.TYPE_RND48;
    }
  
    return {
        identifier: advertiserAddress,
        identifierType: identifierType
    }
  }
docs: Extract the identifier from the given source packet.
  @param {String} packet The source packet as a hexadecimal string.
  @return {Object} The identifier and its type.