Root Cause:

    Not support "priority" on DNS NAT method
Solution:

    Implement "priority" on DNS NAT method

    1. Add "nat protocol dns <priortiy>" CLI command

    2. Add "nat dnspri <vip> <priority>" CLI command to set priority of static NAT entry

Setup llb and nat dns environment
Set nat dns protocol to priority
Set priority to every static NAT entry
Check whether the answers in the DNS response have been rewritten according to the configured priority