Allow NetworkStack permissions in netd

The signature permission held by the NetworkStack is equivalent to all
of CONNECTIVITY_INTERNAL, NETWORK_STACK, USE_RESTRICTED_NETWORKS and
NETWORK_BYPASS_PRIVATE_DNS.

Test: Boots, WiFi working with NetworkStack not having platform
      signature perms

Change-Id: Ibd2be7eae9bbe851467be9be12177ca685a1bf23