Add privapp permissions to network modules.

When built as part of the system, the network stack and the
captive portal login app should have the BYPASS_PRIVATE_DNS
and CONNECTIVITY_USE_RESTRICTED_NETWORKS permissions.
These are necessary to validate restricted networks, bypass VPNs,
bypass private DNS for captive portal login, etc. Add these
permissions to privapp-permissions-platform.xml.

When installed as mainline modules that cannot use signature
permissions, the modules get this ability by virtue of having the
MAINLINE_NETWORK_STACK permissions.

Additionally, add the CONNECTIVITY_USE_RESTRICTED_NETWORKS
permission to the captive portal login app manifest, which did
not contain it.

Bug: 129789428
Test: builds, boots
Test: dumpsys package shows permissions
Change-Id: I632359f7eff09fed71167733ac75824a5aa57894