Previously, the isc_mem_allocate() and isc_mem_free() would be used for
isc_mem_total test, but since we now use the real allocation
size (sallocx, malloc_size, malloc_usable_size) to track the allocation
size, it's impossible to get the test value right. Changing the test to
use isc_mem_get() and isc_mem_put() will use the exact size provided, so
the test would work again on all the platforms even when jemalloc is not
being used.