haproxy: add --haproxy-clientip flag to spoof client IPs

[RaitoBezarius]

This PR enable --haproxy-clientip as per TODO item 5.2 (#5125).

I'm not certain yet I have done the appropriate things yet. I will add tests and docs soon. :)

[RaitoBezarius]

@bagder Hi there, I updated the PR and added some test cases, is there anything else to do so the contribution can be accepted?

[RaitoBezarius]

(I see that my tests needs to be fixed too.)

[bagder]

The test 1912 problem can be fixed with this:

diff --git a/include/curl/typecheck-gcc.h b/include/curl/typecheck-gcc.h
index bc8d7a78c..b880f3dc6 100644
--- a/include/curl/typecheck-gcc.h
+++ b/include/curl/typecheck-gcc.h
@@ -278,10 +278,11 @@ CURLWARNING(_curl_easy_getinfo_err_curl_off_t,
    (option) == CURLOPT_EGDSOCKET ||                                           \
    (option) == CURLOPT_FTP_ACCOUNT ||                                         \
    (option) == CURLOPT_FTP_ALTERNATIVE_TO_USER ||                             \
    (option) == CURLOPT_FTPPORT ||                                             \
    (option) == CURLOPT_HSTS ||                                                \
+   (option) == CURLOPT_HAPROXY_CLIENT_IP ||                                   \
    (option) == CURLOPT_INTERFACE ||                                           \
    (option) == CURLOPT_ISSUERCERT ||                                          \
    (option) == CURLOPT_KEYPASSWD ||                                           \
    (option) == CURLOPT_KRBLEVEL ||                                            \
    (option) == CURLOPT_LOGIN_OPTIONS ||                                       \

[bagder]

The 1139 test failure happens because you have not created a docs/cmdline/haproxy-clientip.d file that documents the command line option (so it is missing from the curl.1 man page). Also add that file name to Makefile.inc and the DPAGES list to make it used in the build.

[RaitoBezarius]

Thank you for the guidance, I have fixed the remaining issues, I am checking the CI on my side but hopefully should be good.
I guess there's some adjustements for the documentation now that we enable --haproxy-protocol by default.
Do you see something else?

[RaitoBezarius]

Hmm, it's unclear to me why 3201/3022 are failing now. Testing manually seems to work.

[RaitoBezarius]

@bagder I addressed the comments, rebased the PR, let me know if I can do anything more. :)

[bagder]

Thanks!