Explicitly require root privs for tests requiring it

These tests currently require root privs to interact with netd:
  resolv_integration_test
  libnetdbpf_test
  netd_unit_test
  netd_integration_test

Bug: 134891412
Test: atest
Change-Id: I3e286fd7e7603e30b4f4d655fe311c35e05fbc78