Port fix from PR 3931

[manamand2020]

What I did

Port the fix from sonic-net/sonic-utilities#3931

How to verify it

Verified original PR on hardware.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[lolyu]

the change looks good to me, do you have data that how long does the new LUA script with nexthop read take?

[manamand2020]

the change looks good to me, do you have data that how long does the new LUA script with nexthop read take?
@lolyu
Nexthop table read time: 2.34 ms (with 128 v6 and 10 v4 nbr on one mux port.)

--- a/scripts/dualtor_neighbor_check.py
+++ b/scripts/dualtor_neighbor_check.py
@@ -148,6 +148,7 @@ for i, neighbor_entry in ipairs(neighbor_entries) do
 end

 -- read ASIC nexthop table
+local nexthop_start_time = redis.call('TIME')
 local nexthop_prefix = asic_state_table_name .. ASIC_DB_SEPARATOR .. 'SAI_OBJECT_TYPE_NEXT_HOP:'
 local nexthop_entries = redis.call('KEYS', nexthop_prefix .. '*')
 for i, nexthop_entry in ipairs(nexthop_entries) do
@@ -164,6 +165,9 @@ for i, nexthop_entry in ipairs(nexthop_entries) do

     asic_nexthop_table[nexthop_id] = nexthop_info
 end
+local nexthop_end_time = redis.call('TIME')
+local nexthop_duration_ms = (nexthop_end_time[1] - nexthop_start_time[1]) * 1000 +
+                           (nexthop_end_time[2] - nexthop_start_time[2]) / 1000

 local result = {}
 result['neighbors']         = neighbors
@@ -173,6 +177,7 @@ result['asic_fdb']          = asic_fdb
 result['asic_route_table']  = asic_route_table
 result['asic_neigh_table']  = asic_neighbor_table
 result['asic_nexthop_table'] = asic_nexthop_table
+result['nexthop_read_time_ms'] = nexthop_duration_ms

 return redis.status_reply(cjson.encode(result))
 """
@@ -356,6 +361,9 @@ def read_tables_from_db(appl_db):
     asic_route_table = tables["asic_route_table"]
     asic_neigh_table = tables["asic_neigh_table"]
     asic_nexthop_table = tables["asic_nexthop_table"]
+    nexthop_read_time_ms = tables.get("nexthop_read_time_ms", 0)
+
+    WRITE_LOG_INFO("Nexthop table read time: %.2f ms", nexthop_read_time_ms)
     WRITE_LOG_DEBUG("neighbors: %s", json.dumps(neighbors, indent=4))
     WRITE_LOG_DEBUG("mux states: %s", json.dumps(mux_states, indent=4))
     WRITE_LOG_DEBUG("hw mux states: %s", json.dumps(hw_mux_states, indent=4))