Enable gen_log for DnsResolverService and fix some style problems

1. enable gen_log in DnsResolverService
2. fix style problems in DnsResolverService
3. fix potential log_func register bug which is service is registered earlier
   than logFunc in NetdNativeService

Test: built, flashed, booted
      system/netd/tests/runtests.sh pass

Change-Id: Ib046b52065f894cd5bac0c9c905b85352556a48d