Bugfix for fixed interfaces.

I now think my last bugfix was incorrect - what we need to change when
the link is flipped is which end we compare, rather than which interface
on the vlink we compare with.

Quite a bear to track down!

assign/score.cc

@@ -1506,6 +1506,17 @@ bool find_best_link(pvertex pv,pvertex switch_pv,tb_vlink *vlink,
 	  continue;
       }
 
+      // XXX: Not 100% sure it's better to do this inside find_best_link rather
+      // than in the caller
+      if (flipped) {
+          // If the endpoints are flipped, then we need to flip our notion of
+          // which ones need to be compared.
+          bool tmp = check_src_iface;
+          check_src_iface = check_dst_iface;
+          check_dst_iface = tmp;
+          SDEBUG(cerr << "         find_best_link: flipping interface comparisons" << endl;)
+      }
+
       SDEBUG(cerr << "         find_best_link: fix_src_iface = " <<
               vlink->fix_src_iface << " check_src_iface = " << check_src_iface
               << " fix_dst_iface = " << vlink->fix_dst_iface
@@ -1518,7 +1529,7 @@ bool find_best_link(pvertex pv,pvertex switch_pv,tb_vlink *vlink,
           // Whether we check the 'source' or 'destination' on the vlink against
           // the phyisical link's source interface depends on whether we're
           // traversing the link if forward or reverse (flipped) order
-          fstring compare_iface = (flipped?vlink->dst_iface:vlink->src_iface);
+          fstring compare_iface = vlink->src_iface;
           if (plink->srciface != compare_iface) {
               SDEBUG(cerr << "          find_best_link (" << vlink->name <<
                       "): Fix source: " << plink->srciface << " != " <<
@@ -1536,7 +1547,7 @@ bool find_best_link(pvertex pv,pvertex switch_pv,tb_vlink *vlink,
       // XXX: This only works because we always have the node as the 'source'
       // of a plink! Shouldn't depend on this!
       if (vlink->fix_dst_iface && check_dst_iface) {
-          fstring compare_iface = (flipped?vlink->src_iface:vlink->dst_iface);
+          fstring compare_iface = vlink->dst_iface;
           if (plink->srciface != compare_iface) {
               SDEBUG(cerr << "          find_best_link (" << vlink->name <<
                       "): Fix dst: " << plink->srciface << " != " <<