Fix bug: Restore sai log levels from LOGLEVEL_DB after saiDiscover

[qiluo-msft]

This bug is introduced from #316 (comment)

The bug is exposed by below steps. The expected log level for SAI_API_SWITCH is SAI_LOG_LEVEL_DEBUG.

admin@sonic:~$ swssloglevel -l SAI_LOG_LEVEL_DEBUG -s -c SWITCH
admin@sonic:~$ redis-cli -n 3 hgetall "SAI_API_SWITCH:SAI_API_SWITCH"
1) "LOGLEVEL"
2) "SAI_LOG_LEVEL_DEBUG"
3) "LOGOUTPUT"
4) "SYSLOG"
admin@sonic:~$ sudo systemctl restart swss
admin@sonic:~$ redis-cli -n 3 hgetall "SAI_API_SWITCH:SAI_API_SWITCH"
1) "LOGLEVEL"
2) "SAI_LOG_LEVEL_DEBUG"
3) "LOGOUTPUT"
4) "SYSLOG"
admin@sonic:~$ sudo grep "loglevel SAI_API_SWITCH" /var/log/syslog
Jul 25 00:00:28.280667 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_DEBUG
Jul 25 00:04:47.411408 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_DEBUG
Jul 25 00:06:31.440304 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_CRITICAL
Jul 25 00:06:31.663183 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_NOTICE

The first syslog line is for swssloglevel
The 3 later syslog lines are for systemctl restart swss

After this fix:

admin@sonic:~$ sudo systemctl restart swss
admin@sonic:~$ sudo grep "loglevel SAI_API_SWITCH" /var/log/syslog
Jul 25 00:10:43.058437 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_DEBUG
Jul 25 00:12:07.920069 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_CRITICAL
Jul 25 00:12:08.133814 sonic NOTICE syncd#syncd: :- saiLoglevelNotify: Setting SAI loglevel SAI_API_SWITCH to SAI_LOG_LEVEL_DEBUG

The 3 syslog lines are for systemctl restart swss

[pavel-shirshov]

@yxieca patch for 201811 should be

pavelsh@pavelsh-vm:~/disk2/public/sonic-buildimage/src/sonic-sairedis$ git diff
diff --git a/syncd/syncd.h b/syncd/syncd.h
index 9ce4dc4..207fa56 100644
--- a/syncd/syncd.h
+++ b/syncd/syncd.h
@@ -141,4 +141,6 @@ void set_sai_api_log_min_prio(
 
 bool enableUnittests();
 
+void set_sai_api_loglevel();
+
 #endif // __SYNCD_H__
diff --git a/syncd/syncd_saiswitch.cpp b/syncd/syncd_saiswitch.cpp
index e90369f..ab6a5d5 100644
--- a/syncd/syncd_saiswitch.cpp
+++ b/syncd/syncd_saiswitch.cpp
@@ -971,7 +971,7 @@ void SaiSwitch::helperDiscover()
 
         saiDiscover(m_switch_rid, m_discovered_rids);
 
-        set_sai_api_log_min_prio("SAI_LOG_LEVEL_NOTICE");
+        set_sai_api_loglevel();
     }
 
     SWSS_LOG_NOTICE("discovered objects count: %zu", m_discovered_rids.size());