Fix for bug 830.

Fixed bugs in getUnsigned methods of NetUtils class.

 * Fixed bugs that getUnsignedByte(byte) and getUnsignedShort(short)
   handled 0 incorrectly.
 * Added tests for getUnsignedByte(byte) and getUnsignedShort(short).

Change-Id: Ie67fb5c07bed31d16d4a52068dda7735fb7cd5e2
Signed-off-by: Hideyuki Tai <h-tai@cd.jp.nec.com>
(cherry picked from commit 37d7a25950e5132d7dabfe4a66d81becbc6ef4dd)