Fix TetheredClient callback fail in InProcessTethering

TetheredClient callback would additional check whether caller has
NETWORK_SETTINGS or {MAINLINE_}NETWORK_STACK permission, but it do not
grant for self accessing. InProcessTethering run in system server, so
the services in system server would fail to call TetheredClient callback.
Grant permission for self process.

Bug: 169231588
Test: atest CtsTetheringTest
Change-Id: Ic04e44aef4df772c718ff25ed331bf02f5940c1d