Enable checks for MANAGE_TEST_NETWORKS in TestNetworkService

This commit re-enables enforcement of the MANAGE_TEST_NETWORK
permission, which is only granted to the shell. CTS tests using this
permission should use UiAutomation.adoptShellPermissionIdentity() to
gain access.

Bug: 72950854
Test: IPsec CTS tests using this passing
Change-Id: I98573a5c68e45abbbaddef01f6ac74a6a18e26f9
Merged-In: I98573a5c68e45abbbaddef01f6ac74a6a18e26f9
(cherry picked from commit 3ec38dc5)