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
Merged-In: Id96d581acb3fa4e52ca62dd94ec257f56bd3a1ce
Change-Id: Id96d581acb3fa4e52ca62dd94ec257f56bd3a1ce
(clean cherry-pick from internal branch)