Revert "Revert "Update VPN capabilities when its underlying network set is null.""

This reverts commit 6a050c7c.

Reason for revert: Retargeted for June monthly release

Bug: 119129310

Change-Id: I9d543415c5707859cfa2a14a1a8ce5909aae7d11
Merged-In: Id0abc4d304bb096e92479a118168690ccce634ed