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>
Merge "Fixed bugs in getUnsigned methods of NetUtils class."