implement of getNetAddr and getBroadCastAddr.
green, add new test for getNetAddr and getBroadCastAddr.
modify the getBroadCastAddr to pass the new test.
add net tdd test.
实现需求：
	1. 不能存在 *.*.*.0 / *.*.*.255
	2. 不能存在127.*.*.*
1. net test. passed.
2. refactor getNetAddr.
red, add new test for isIpMaskValidate.
implement isIpMaskValidate to pass the test.
green, pass the new test, for ip = mask and ip = normal.
refactor getNetAddr by extract method.
refactor the getBroadCastAdd function using the extracted method.