dns: Move operator<<
dns: Move operator<<

The operator<< for opt_family should follow the opt_family definition,
otherwise fmt:: compat doesn't recognize it and asks for formatter.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

dreamsxin/seastar,avikivity/seastar,dreamsxin/seastar,avikivity/seastar,cloudius-systems/seastar,dreamsxin/seastar,avikivity/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar,cloudius-systems/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar