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
Bug: 136633978
Test: atest

Merged-In: Ib7387d83d0da5dde0ee43a164ee01989a458ae8a
(cherry picked from commit 4d89d8bda75c3e9dd05da494c284ec791545f64e)

Change-Id: I7c61ab2d68437c31339a5950f308b33cd2f1d8d6