net: tipc: prepare attrs in __tipc_nl_compat_dumpit()

__tipc_nl_compat_dumpit() calls tipc_nl_publ_dump() which expects
the attrs to be available by genl_dumpit_info(cb)->attrs. Add info
struct and attr parsing in compat dumpit function.

Reported-by:  <syzbot+8d37c50ffb0f52941a5e@syzkaller.appspotmail.com>
Fixes: 057af707

 ("net: tipc: have genetlink code to parse the attrs during dumpit")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>