code: function decodeLength(s) {
  	var size = new type.UInt8().read(s).value;
  	if(size & 0x80) {
  		size &= ~0x80;
  		if(size === 1) {
  			size = new type.UInt8().read(s).value;
  		}
  		else if(size === 2) {
  			size = new type.UInt16Be().read(s).value;
  		}
  		else{
  			throw new error.ProtocolError('NODE_RDP_ASN1_BER_INVALID_LENGTH');
  		}
  	}
  	return size;
  }
docs: Parse length(L) field of BER TLV
  @param s {type.Stream}
  @returns {integer}