reactor: workaround tmpfs O_DIRECT vs O_EXCL bug
reactor: workaround tmpfs O_DIRECT vs O_EXCL bug

On tmpfs, creating files with O_DIRECT fails, but after the file was
created.  This means that our re-open attempt that drops O_DIRECT will
fail if O_EXCL was specified.

Fix by dropping O_EXCL too.  This can fail if the file existed before,
but our relaxed dma mode is a hack anyway.

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