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
Change-Id: Ic8d45b802d72a266f9ec97bfea620c1ede6967e5