bgpd: Fix AS_PATH size calculation for long paths

If you have an AS_PATH with more entries than
what can be written into a single AS_SEGMENT_MAX
it needs to be broken up.  The code that noticed
that the AS_PATH needs to be broken up was not
correctly calculating the size of the resulting
message.  This patch addresses this issue.

bgpd/bgp_aspath.c

@@ -903,7 +903,7 @@ aspath_put (struct stream *s, struct aspath *as, int use32bit )
               assegment_header_put (s, seg->type, AS_SEGMENT_MAX);
               assegment_data_put (s, seg->as, AS_SEGMENT_MAX, use32bit);
               written += AS_SEGMENT_MAX;
-              bytes += ASSEGMENT_SIZE (written, use32bit);
+              bytes += ASSEGMENT_SIZE (AS_SEGMENT_MAX, use32bit);
             }
 
           /* write the final segment, probably is also the first */