Summary
-------
Clarifies the behaviour of the `setSoTimeout()` method when given a negative `timeout` value. 

Problem
-------
With this option set to a non-zero `timeout`, a call to `receive()` for this DatagramSocket will block for the specified time. Any value less than zero is invalid, and as such, should throw an `IllegalArgumentException`. However, `setSoTimeout()` does not specify what happens if given a negative `timeout` value.

Solution
--------
The solution is to document that a negative `timeout` value will result in an `IllegalArgumentException` being thrown. As the `setSoTimeout()` method already throws an `IllegalArgumentException`, this change is effectively documenting existing long-standing behaviour. 

However, an explicit check on negative values will now be made in the `setSoTimeout()` method to avoid dependence on implementation for such a check to occur. 

Specification
-------------
 src/java.base/share/classes/java/net/DatagramSocket.java

          *
          * @param timeout the specified timeout in milliseconds.
          * @throws SocketException if there is an error in the underlying protocol, such as an UDP error.
    +    * @throws IllegalArgumentException if {@code timeout} is negative
          * @since   1.1
          * @see #getSoTimeout()
          */
         public synchronized void setSoTimeout(int timeout) throws SocketException {... }

Webrev:
http://cr.openjdk.java.net/~pconcannon/8222829/webrevs/webrev.02/