net: http: Fix __z_http_service_define fields incorrectly ordered C++20

[Pavllick]

Instance of the http_service_desc struct created by the __z_http_service_define macro uses designated initializer with fields not following original http_service_desc struct order which lead to compile time exception when #include <zephyr/net/http/service.h> is included and project is compiled for C++20.

.../zephyr/include/zephyr/net/http/service.h:113:9: error: designator order for field 'http_service_desc::backlog' does not match declaration order in 'const http_service_desc'
  113 |         }
      |         ^
.../zephyr/include/zephyr/net/http/service.h:195:9: note: in expansion of macro '__z_http_service_define'
  195 |         __z_http_service_define(_name, _host, _port, _concurrent, _backlog, _detail,               \
      |         ^~~~~~~~~~~~~~~~~~~~~~~

As C++20 doesn't allow out-of-order designated initialization.

This PR fixes the order.

[github-actions]

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[dkalowsk]

Thanks for the fix @Pavllick !

[github-actions]

Hi @Pavllick!
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