packet: mark methods noexcept
packet: mark methods noexcept

Mark all non-throwing methods noexcept.
This makes the output_stream api noexcept easier.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

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