Define struct iphdr for OSX

Use FreeBSD struct iphdr definition for OSX also. From the commentary in
the source file:
On BSD the IPv4 struct is called struct ip and instead of iXX
the members are called ip_XX. One could change this code to use
struct ip but that would require to define _BSD_SOURCE and that
might have other complications. Instead make sure struct iphdr
is present on FreeBSD.
1 file changed