disabled including <netinet/in_systm.h> <netinet/ip.h> <netinet/ip_var.h> by #if 0.
disabled including
<netinet/in_systm.h>
<netinet/ip.h>
<netinet/ip_var.h>
by #if 0.

These seem to be unnecessary to compile ping6. This is the case for fbsd3.
please check on other platforms. If it's ok for all OSes, then I'll completely
nuke the part.

MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame