Add VPN name into the extra info of NetworkInfo

Add the extra info of a VPN network to provide helpful
debugging info.

The validation logs in the dumpsys of NetworkStack refer to
the extra info from NetworkInfo of the given network.
But the extra info in a VPN NetworkInfo is empty so the name
will be null. It's hard to tell the exact name information
from only dumpsys of NetworkStack.

Bug: 297790570
Test: atest FrameworksNetTests
Change-Id: I7cf5f30db9a9bbc0361e5dc6bf4d8f533e12f5c8