1. Previously, getDnsNetId doesn't handle all the cases.
Fix it with cosidering bypass private DNS flag.
2. Make getDnsNetId return Network instead of netId,
and change name from getDnsNetId to getDnsNetwork
Bug: 129530368
Test: atest DnsResolverTest DnsUtilsTest
Merged-In: Ibb5080acd3c296650d56532fc7da525e9fa95e8f
(cherry picked from commit 3854966dc9)
Change-Id: I37353642088bcc17da0cf17f78a5ed9efc9aefc3
459a5becd9