vlib_zero_combined_counter (&lm->counter_main, counter_index);
vlib_zero_combined_counter (&lm->counter_main, counter_index+1);
nincr++;
vlib_zero_combined_counter (&lm->counter_main, counter_index);
vlib_zero_combined_counter (&lm->counter_main, counter_index+1);
nincr++;