elements/CoDel: convert from raw division to int_divide

The compiler was promoting some of the operations here to wider types.  This
meant that a kernel module with CoDel would fail to link against __divdi3.

Instead, use the helper functions in click/integers.hh

Signed-off-by: Derrick Pallas <pallas@meraki.com>
Merge pull request #148 from pallas/fix-codel-linuxmodule

elements/CoDel: convert from raw division to int_divide