qed: Clear dcbx memory buffers before the usage.

This patch takes care of clearing the uninitialized buffer before using it.
1. pfc pri-enable bitmap need to be cleared before setting the requested
   enable bits. Without this, the un-touched values will be merged with
   requested values and sent to MFW.
2. The data in app-entry field need to be cleared before using it.
3. Clear the output data buffer used in qed_dcbx_query_params().

Signed-off-by: Sudarsana Reddy Kalluru <sudarsana.kalluru@qlogic.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>