Fix a possible flake in disconnectFromWiFi

1. There is a theoretical issue where the callback is not yet
   registered when wifi is disabled, but there is no evidence
   of it actually happening
2. 2 minutes timeout makes no sense for these tests that have a
   total 1 minute timeout anyway

Bug: 196387278
Test: CtsNetTestCases
Change-Id: I120af9b312ca34431d0e62dd85233fcdaa1b09b9
2 files changed