Perform VPN data stall recovery on unvalidated VPN network

This commit stops relying on data stall detection event for VPN
network recovery. Data stall detection will also result in an
unvalidated result, so VPN is not necessary to listen to data
stall event to perform the recovery. When VPN receives network
validation failure event, VPN will try to perform recovery
starting from MOBIKE to session reset after this change.

This helps to recover the stalls that are not detected or
triggered by data stall detection, e.g. A stall happens when
the VPN underlying network is switched. System triggers the
reevaluation. If the validation fails, data stall mechanism
will not be triggered and result in no recovery in VPN.

Bug: 289746779
Test: atest FrameworksNetTests
Change-Id: Ibb8197a689220db5868f351bffa9ac27334355e2