Cleanup p2p0 interface upon tearDownInterfaces().

Cleanup p2p0 interface upon tearDownInterfaces().

This replaces NetlinkUtils::GetInterfaceInfo with NetlinkUtils::
GetInterfaces. Instead of picking client interface inside NetlinkUtils,
this change allows wificond main object(server) to dump all the interfaces
from kernel.
Being able to dump all interfaces, wificond main object therefore can mark
down all the interfaces upon cleanup.

Bug: 36139978
Bug: 35949498

Test: compile, unit tests, manual test, integration test

Change-Id: I66dd4f8c3b26087dd182591763de8fa4da29f1d6