scylla-gdb.py: Print the pointers of elements in boost_intrusive_list_printer
scylla-gdb.py: Print the pointers of elements in boost_intrusive_list_printer

Sometimes it is helpful to print the pointers of the object in the list.

For example:

(gdb) p debug::repair_meta_for_masters._repair_metas

$1 = boost::intrusive::list of size 3 = [0x6000051df830, 0x60000221f830, 0x60000473f830] = [@0x6000051df830={
  _db = @0x7fffe538c9f0,
  _messaging = @0x7fffe538ca90,
  _cf = @0x6000066f0000,
  _schema = {
    _p = 0x600006568700
  },
  _range = {

  ...

(gdb) p debug::repair_meta_for_followers._repair_metas

$2 = boost::intrusive::list of size 3 = [0x60000081a808, 0x60000432b008, 0x60000432a808] = [@0x60000081a808={
  _db = @0x7fffe538c9f0,
  _messaging = @0x7fffe538ca90,
  _cf = @0x6000066f0000,
  _schema = {
    _p = 0x600006568700
  },

  ...

Refs #7103

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