Perform a mathematical operation on an extracted value and a specified
value or existing variable, and store the outcome in a new resulting
variable. These resulting variables can be referenced later in the
rule, at the same places as byte_extract variables. 

The syntax for this rule option is different. The order of the options 
is critical for the other rule options and can't be changed. For
example, the first option is the number of bytes to extract.
Here the name of the option is explicitly written, for example : bytes 2.
The order is not important.

NOTE: Byte_math operations are performed on unsigned 32-bit values. When 
      writing a rule it should be taken into consideration to avoid wrap around.

===== Examples

  alert tcp ( byte_math: bytes 2, offset 0, oper *, rvalue 10, result area; 
     byte_test:2,>,area,16;)

At the zero offset of the payload, extract 2 bytes and apply multiplication operation with
value 10. Store result in variable area. The area variable is given as
input to byte_test value option.

Let's consider 2 bytes of extracted data is 5. The rvalue is 10.
Result variable area is 50 ( 5 * 10 ).
Area variable can be used in either byte_test offset/value options.
