Add TETHER_PRIVILEGED permission to shell for CTS test.

Grant TETHER_PRIVILEGED permissions to the shell identity
for use within CTS tests.

Bug: 145490751
Test: atest CtsTetheringTest
Change-Id: Ifad265cdc5e0b1b1b2fa8f4f79eeb7dd18493624
Merged-In: Ifad265cdc5e0b1b1b2fa8f4f79eeb7dd18493624