proposal. This only affects Nmap's root directory. We might also need to
modify the code which autogenerates Nmap's source code files such as IPv6
fingerprinting code.
This was failing to compile to platforms where HAVE_STRUCT_IP is true
but HAVE_STRUCT_ICMP is false, because struct ip was not being defined
(by a system header) before struct icmp.
The comment in struct_ip.h explains the reasoning for this. The AIX C library
uses #defines that change the names of members of struct ip, and conflict with
some existing code. (Notably struct ip_hdr in libdnet and IPv4Header::h in
libnetutil.) We can still use the AIX files if we include <netinet/ip.h> after
this other code has been preprocessed. That's hard to enforce when
<netinet/ip.h> is included from another header file; this new file allows
including it always late, and only where needed.
