Skip the legacy stats recording if DNS requests are denied by network policy

In order to prevent the false INTERNAL_ERROR event which is caused by
network policy fill up the legacy DNS stats, skip adding new legacy DNS
stats when we got errno == EPERM.

Bug: 151166599
Test: atest
Change-Id: I4c1d2a5c9f43650a5346a5ee0bb88eb36f850096