Change reuseable_* to reusable_* .
Currently only the Lease* structure has 2 parameters using the wrong spelling of reusable_:
uint32_t reuseable_valid_lft_;
uint32_t reuseable_preferred_lft_;
As the Lease is internal to Kea, this should be easy to do without impacting clients. The only affected 'external' functionality could be the user hook libraries.