fix bugs:
1.change max valid domain length from 254 to 253
2.domain search with last dot bug
3.invalid ipv6 validation,eg:2001:6a8:0:1:210:4bff
4.ip format when search ns by ip
refactor:add domain length validation,domain without last dot length >=3
and <=253
Merge pull request #211 from forumbyr/master

fix bugs: see commit detail