bnxt_en: Add DCBNL DSCP application protocol support.

Expand the .ieee_setapp() and ieee_delapp() DCBNL methods to support
DSCP.  This allows DSCP values to user priority mappings instead
of using VLAN priorities.  Each DSCP mapping is added or deleted one
entry at a time using the firmware API.  The firmware call can only be
made from a PF.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>