file_desc: return a file_desc object from a fd number
file_desc: return a file_desc object from a fd number

io_uring will need this, since accept() return a file
descriptor

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

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