Correctly check permission and app identity for tethering

Have the caller pass its package name. Appops will check
that the UID belongs indeed to the package name, and that
the UID has the requisite permissions.

Also add WRITE_SETTINGS to the bluetooth process.

Bug: 134649258
Test: atest PanServiceTest
Change-Id: I6cf29c36cf6e7229abb5be4a108efb9b9600217d
(cherry picked from commit f0ae367fa83ee3b2880971af7f1325e568f56677)