[ns] addition to ip hdr

["A. Jain" <Amit.Jain@sophia.inria.fr>]

hi nsusers,

I am doing some simulation for which i need to add some fields in ip
header.

I want to know whether I can do it by just adding the fields in "struct
hdr_ip" or I will have to make some other changes too.

Becaoz I tried just adding some fields in Ip header. And it works
perfectly fine when application is run on udp agent but not when run on
tcp agent. I suppose may be some problem with hdrs becoz there is no udp
hdr but there is tcp hdr. 

Kindly mail me the suggestions. 

Regards
amit