genfs_contexts

/proc/net/xt_qtaguid is used by apps to track their network data
use. Limit access to just zygote spawned processes - apps and
system_server, omitting access to isolated_app which is not allowed
to create network sockets.
As Android moves to eBPF for app's network data stats, access to
/proc/net/xt_qtaguid will be removed entirely. Segmenting access off
is the first step.
Bug: 68774956

This change also helps further segment and whitelist access to
files in /proc/net and is a step in the lockdown of /proc/net.
Bug: 9496886

Test: boot Taimen. Walk through setup-wizard. Make phone call and
    video call. Browse web. Watch youtube. Navigate in maps.
Test: cts-tradefed run cts -m CtsAppSecurityHostTestCases -t \
    android.appsecurity.cts.AppSecurityTests
Test: cts-tradefed run cts -m CtsNativeNetTestCases
Test: cts-tradefed run cts -m CtsIncidentHostTestCases -t \
    com.android.server.cts.NetstatsIncidentTest
Test: cts-tradefed run cts -m CtsOsTestCases -t \
    android.os.cts.StrictModeTest
Test: cts-tradefed run cts -m CtsNetTestCases -t \
    android.net.cts.TrafficStatsTest
Test: cts-tradefed run cts -m CtsUsageStatsTestCases -t \
    android.app.usage.cts.NetworkUsageStatsTest
Test: vts-tradefed run vts -m VtsQtaguidTest
Change-Id: Idddd318c56b84564142d37b11dcc225a2f2800ea