isisd: Correct Valgrind errors

isisd: Correct Valgrind errors

Runing most of isisd tests with --valgrind-memleaks give many memory errors.
This is due to the way isisd is stopped: performing a "no router isis XXX"
through CLI solves most of them. Indeed, isis_finish() doesn't call
isis_area_destroy() leaving many allocated memory unfreed.

This patch adds call to appropriate delete function or XFREE() when necessary to
properly free all alocated memory before terminating isisd.

Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>