Not defer network disconnect event in Probing state

If network reevaluation is triggered just before network
disconnect, statemachine will stuck in Probing state and unable
to exit.

Test: 1. runtest frameworks-net
      2. connect and disconnect wifi to see if NetworkMonitor is
         destroyed as expected
Bug: 119158436

Change-Id: Ibbb20caee94d0a5ab5403c6b01636936025562fe