Handle missing parent interfaces

While this does not fix having inconsistent interfaces, at least we
don't fail enumerating them. With this change we still return these
children interfaces without parent set.

Bug: 159277702
Test: atest CtsLibcoreTestCases:libcore.java.net.NetworkInterfaceTest
Change-Id: Ibbe1f273683eb169a0e96425a2c21c5072bf19d7
2 files changed