net.http: set IP address for HTTP server during tests

[lcheylus]

On OpenBSD, TCP connect fails (return EINVAL) if attempted with 0.0.0.0 address.

In vlib/net/http/server_test.v, for tests test_server_custom_handler and test_host_header_sent_to_server, use 127.0.0.1 as IP addr for the HTTP server.

Fix #22126

Tests OK on OpenBSD/amd64 and Linux/amd64 with tcc, clang and gcc

$ ./v test vlib/net/http/server_test.v 
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 OK    1996.242 ms vlib/net/http/server_test.v
--------------------------------------------------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 3590 ms, on 1 job. Comptime: 1585 ms. Runtime: 1996 ms.

$ ./v -cc clang test vlib/net/http/server_test.v 
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 OK    2112.866 ms vlib/net/http/server_test.v
--------------------------------------------------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 5325 ms, on 1 job. Comptime: 3206 ms. Runtime: 2112 ms.

$ ./v -cc egcc test vlib/net/http/server_test.v 
---- Testing... ----------------------------------------------------------------------------------------------------------------------------
 OK    2044.330 ms vlib/net/http/server_test.v
--------------------------------------------------------------------------------------------------------------------------------------------
Summary for all V _test.v files: 1 passed, 1 total. Elapsed time: 6186 ms, on 1 job. Comptime: 4136 ms. Runtime: 2044 ms.

[huly-for-github]

Connected to Huly®: V_0.6-23053

[JalonSolov]

Believe it or not, some versions of Windows do not set 127.0.0.1 in their hosts file, so this could break on them.

This change will also be a problem on systems with IP6 as the default/only scheme.

[lcheylus]

Believe it or not, some versions of Windows do not set 127.0.0.1 in their hosts file, so this could break on them.

No issue in Windows CI with my fix :)

This change will also be a problem on systems with IP6 as the default/only scheme.

This fix is only for tests of HTTP server. I doubt any serious developer would use a system with only an IPv6 stack.

So I think that my fix is not a problem. And it allows that every test runned with VTEST_JUST_ESSENTIAL are OK on OpenBSD (proposal to add a specific CI for OpenBSD soon...).

[spytheman]

We can make the ip setting conditional on the platform, if there are problems in the future.
Imho it is a good change, since it will allow more checks (an OpenBSD CI), with a small chance of breaking the test for non CI users.

[spytheman]

use_net_and_net_unix_together_test.v seems to be stuck on the gcc-windows job, but that is unrelated to the PR.