packet: introduce release() and release_into()
packet: introduce release() and release_into()

Allows breaking up a packet into a bunch of temporary_buffers, sharing
a deleter.

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