For local communications (npipe://, unix://), the hostname is not used,
but we need valid and meaningful hostname.
The current code used the client's `addr` as hostname in some cases, which
could contain the path for the unix-socket (`/var/run/docker.sock`), which
gets rejected by go1.20.6 and go1.19.11 because of a security fix for
[CVE-2023-29406 ][1], which was implemented in https://go.dev/issue/60374.
Prior versions go Go would clean the host header, and strip slashes in the
process, but go1.20.6 and go1.19.11 no longer do, and reject the host
header.
This patch introduces a `DummyHost` const, and uses this dummy host for
cases where we don't need an actual hostname.
Signed-off-by: jingxiaolu <lujingxiao@huawei.com>
