VMCI: Doorbell create and destroy fixes

VMCI: Doorbell create and destroy fixes

This change consists of two changes:

1) If vmci_doorbell_create is called when neither guest nor
   host personality as been initialized, vmci_get_context_id
   will return VMCI_INVALID_ID. In that case, we should fail
   the create call.
2) In doorbell destroy, we assume that vmci_guest_code_active()
   has the same return value on create and destroy. That may not
   be the case, so we may end up with the wrong refcount.
   Instead, destroy should check explicitly whether the doorbell
   is in the index table as an indicator of whether the guest
   code was active at create time.

Reviewed-by: Adit Ranadive <aditr@vmware.com>
Signed-off-by: Jorgen Hansen <jhansen@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>