future-util: Rename futurize_apply_if_func
future-util: Rename futurize_apply_if_func

It is now named futurize_invoke_if_func for consistency with
futurize_invoke.

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

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