future: Move code from do_wait to wait
future: Move code from do_wait to wait

No do_wait is only called when we are sure we want to wait. It also
doesn't need to access _state.

Signed-off-by: Rafael Ávila de Espíndola <1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>

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