[Bro] include icmp6.h problem

[Vern Paxson]

> Actually I just need it in Sessions.cc (for the switch on the ICMP type) 
> so I will use the #undef solution : it's less ugly than keeping a 
> modified version of icmp6.h.

I think you misunderstood me.  If you just need it in Sessions.cc, then
just include it in Sessions.cc rather than in net_util.h (and include it
after DNS-binpac.h, with a comment, if that's the only conflict).  A little
better than using an #undef.

		Vern