p2p: revise tethering handler for shared group interface support

When leaving a group, all information are erased and no group interface
is passed to tethering service.
For separate group interface, tethering could be stopped
on p2p group interface removed. For shared group interface,
i.e. management interface and group interface share one
interface, ex. p2p0, tethering has no chance to be stopped since management
interface won't be removed after leaving a group.

Bug: 141382930
Test: atest FrameworksNetTests
Test: atest FrameworksWifiTests
Test: atest TetheringTests
Change-Id: Ib611018b67c76ff79c7e6658136721090feb145b