Adding permission for Ethernet Network Management

Adding MANAGE_ETHERNET_NETWORKS as a signature level permission
to allow an application to dynamically change ethernet network values.

Bug: 210485380
Test: atest EthernetServiceTests
Change-Id: Icf9c2accc86735cc981adc0d5a24802e0616ffaf
Merged-In: Icf9c2accc86735cc981adc0d5a24802e0616ffaf