Currently if the user sets an odd value for [tx|rx]-usecs we align the
value because the hardware only understands ITR values in multiples of
2. This seems misleading because we are essentially telling the user
that the ITR value is odd, when in fact we have changed it internally.
Fix this by reporting that setting odd ITR values is not allowed.

Also, while making changes to ice_set_rc_coalesce() I noticed a bit of
code/error duplication. Make the necessary changes to remove the
duplication.
Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>