file_impl: Hide alignment fields
file_impl: Hide alignment fields

They all have getters in class file, so no need to export them directly,
but need to make class file a friend for access.

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

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