generate_dump: add interface FEC stats (sonic-net#4093)

Add FEC stats to the tarball produced by "show tech". The stats can
be found in files named "interface.counters.fec-stats_$idx".

Signed-off-by: Fraser Gordon <[email protected]>
Signed-off-by: Ramesh Raghupathy <[email protected]>

Author: fraserg-arista

scripts/generate_dump

@@ -2306,6 +2306,7 @@ save_counter_snapshot() {
 
     save_cmd "echo $counter_t" "date.counter_$idx"
     save_cmd "show interface counters" "interface.counters_$idx"
+    save_cmd "show interface counters fec-stats" "interface.counters.fec-stats_$idx"
     if ! $IS_SUPERVISOR; then
        save_cmd "show queue counters" "queue.counters_$idx"
     fi