#77 Patch for NetBSD support for vde2

[Olaf Seibert]

I have made some changes so that vde2 can be compiled on NetBSD.
I have not been able to test it yet; I have to look into that.

A summary of the changes:

• mkostemps is not portable
• setpgrp is used unportably
• added VDE_NETBSD in most places where there is already a VDE_FREEBSD
• a header had an incorrect include guard

• include "config.h" added for some files, to actually pick up VDE_*BSD

• some ICMP_* names are apparently spelled differently on NetBSD