Get NetworkCapabilities from NetworkCallback

Register network callback for all networks and record
NetworkCapabilities for every networks. Once onDnsEvent is
triggered, use the netId it passes in to find the corresponding
NetworkCapabilities instead of using netId to create a Network
object(hidden API) then get the NetworkCapabilities by
ConnectivityManager#getNetworkCapabilities.

Bug: 182963397
Test: m
Test: atest IpConnectivityMetricsTest
Test: atest NetdEventListenerServiceTest
Change-Id: I91d68ca33253831b78def1ddeb074ba944a5d6ad
Merged-In: I91d68ca33253831b78def1ddeb074ba944a5d6ad
  (cherry-picked from ag/13959432)