crypto/qat: improve DOCSIS session creation

crypto/qat: improve DOCSIS session creation

This patch improves the DOCSIS session creation as follows:
- it validates the security action type as well as the protocol before
  creating a session and now does this validation before allocating the
  session from the mempool
- it clears the entire private session struct before populating it with
  DOCSIS session info, in case any data was left over from the last time
  it was used
- it simplifies the DOCSIS parameter setting, which was overly
  complicated

Fixes: 6f0ef237404b ("crypto/qat: support DOCSIS protocol")
Signed-off-by: David Coyle <david.coyle@intel.com>
Acked-by: Fiona Trahe <fiona.trahe@intel.com>