Wrong iphdr and tcphdr mapping

[dthaler]

Describe the bug

l3af-project/eBPF-Package-Repository#54 is failing which tries to use iphdr and tcphdr in cross-platform code.

https://github.com/microsoft/ebpf-for-windows/blob/main/include/net/ip.h#L94 defines it as _IPV4_HEADER, but the field names in that struct don't match the expected field names in iphdr which is causing the windows test failures in l3af-project/eBPF-Package-Repository#54.

OS information

No response

Steps taken to reproduce bug

Try to compile l3af-project/eBPF-Package-Repository#54

Expected behavior

Build should succeed

Actual outcome

Build fails

Additional details

D:/a/eBPF-Package-Repository/eBPF-Package-Repository/ratelimiting/ratelimiting_kern.c(103,27): error G1A4676F8: no member named 'ihl' in 'struct _IPV4_HEADER' [D:\a\eBPF-Package-Repository\eBPF-Package-Repository\build\ratelimiting\ratelimiting_kern.vcxproj]
      __u8 l4_offset = iph->ihl * 4; // ipv4 header length
                       ~~~  ^
D:/a/eBPF-Package-Repository/eBPF-Package-Repository/ratelimiting/ratelimiting_kern.c(114,31): error G1A4[67](https://github.com/l3af-project/eBPF-Package-Repository/actions/runs/5384061159/jobs/9771541350?pr=54#step:5:68)6F8: no member named 'doff' in 'struct tcphdr' [D:\a\eBPF-Package-Repository\eBPF-Package-Repository\build\ratelimiting\ratelimiting_kern.vcxproj]
      __u16 data_offset = tcph->doff * 4; // tcp header length
                          ~~~~  ^

https://github.com/microsoft/ebpf-for-windows/blob/main/include/net/tcp.h#L11 has data_offset instead of doff

[hawkinsw]

@dthaler Do you want to add Linux-compatible field names for the IPv6 header, too, while we are at it?