Adding permission for OEM managed preferences

Adding CONTROL_OEM_PAID_NETWORK_PREFERENCE as a signature level
permission to allow an application to control OEM managed network
preferences.

Bug: 176496438
Bug: 176494815
Test: atest FrameworksNetTests
atest NetworkStackTests
atest FrameworksNetIntegrationTests
atest NetworkStackIntegrationTests
atest CtsNetTestCasesLatestSdk
Change-Id: Iee13e89f3931c7079c2d88cb57b249b1b1cf93ad

Change-Id: Id29cafe1eaf5dff8a0605cb2579204d9c77b7e70