Fix the vulnerability of mbed-os #15462 issue #374
                
     Merged
            
            
          
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Based on
ARMmbed#15474
Summary of changes
Set the stateRx variable to HCI_RX_STATE_IDLE when an invalid HCI packet type is detected, to prevent overflow in the hdrRx buffer.
Impact of changes
Migration actions required
Documentation
Pull request type
[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)
Test results
[] No Tests required for this change (E.g docs only update)
[X] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR