Support putting one Ethernet interface in server mode.

requestTetheredInterface can be used to put an interface in server mode,
which will persist until release() is called on the returned request, or
until the requesting process dies.

Test: Enabled ethernet tethering with change on top
Bug: 130840861
Change-Id: Id96d581acb3fa4e52ca62dd94ec257f56bd3a1ce
3 files changed