Suppress ARP Lookup in ns-2

Sometimes, it is annoying to see packets drop due to ARQ failures (showed as IFQ ARP in traces). Here is a quick fix, define a new variable trivial_mode_ in Arp.h. When it is on, the ARP lookup and query procedure is suppressed and a number as same as IP id will be used as MAC id.

Related codes in arp.cc:

ARPTable::ARPTable(const char *tclnode, const char *tclmac):
 LinkDelay(),trivial_mode_(0){
 LIST_INIT(&arphead_);
        node_ = (MobileNode*) TclObject::lookup(tclnode);
 assert(node_);

 mac_ = (Mac*) TclObject::lookup(tclmac);
 assert(mac_);
 LIST_INSERT_HEAD(&athead_, this, link_);
        //adding a mode to avoid ARP procedure
        bind ("trivial_mode_", &trivial_mode_);
}

ARPEntry*
ARPTable::arplookup(nsaddr_t dst)
{
 ARPEntry *a, *llinfo;

 for(a = arphead_.lh_first; a; a = a->nextarp()) {
  if(a->ipaddr_ == dst)
   return a;
 }
        if (!trivial_mode_)
           return 0;
        else{
         llinfo = new ARPEntry(&arphead_, dst);      
                assert(llinfo);
         llinfo->macaddr_ = int(dst);
         llinfo->up_ = 1;      
                return llinfo;
 }
           
}