ice: Fix problems with DSCP QoS implementation

The patch that implemented DSCP QoS implementation removed a
bandwidth check that was used to check for a specific condition
caused by some corner cases.  This check should not of been
removed.

The same patch also added a check for when the DCBx state could
be changed in relation to DSCP, but the check was erroneously
added nested in a check for CEE mode, which made the check useless.

Fix these problems by re-adding the bandwidth check and relocating
the DSCP mode check earlier in the function that changes DCBx state
in the driver.

Fixes: 2a87bd73 ("ice: Add DSCP support")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>