gdb: Fix 'scylla ptr' reporting large object pages as free
gdb: Fix 'scylla ptr' reporting large object pages as free

The 'free' attribute is not updated for all pages belonging to a large
object, so we can't use it to determine if the page is allocated or
not. More reliable way is to check if it belongs to any free span.
Message-Id: <b7337dd737fed0b655d7dd4fb6b95735cbac2506@scylladb.com>

avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,duarten/scylla