[acl]: Fix crash in ACL counters thread. (sonic-net#203)

* Revert "[aclorch]: Temporarily disable ACL thread of collecting counters (sonic-net#202)"

This reverts commit 2f594c7.

* [acl]: Fix crash in ACL counters thread.

Due to incorrect usage of thread class and race conditions
from time to time conter thread was accessing AclOrch
object members before thay were initialized.

Author: oleksandrivantsiv

orchagent/aclorch.cpp

@@ -817,6 +817,10 @@ AclOrch::AclOrch(DBConnector *db, vector<string> tableNames, PortsOrch *portOrch
     }
 
     m_mirrorOrch->attach(this);
+
+    // Should be initialized last to guaranty that object is
+    // initialized before thread start.
+    m_countersThread = thread(AclOrch::collectCountersThread, this);
 }
 
 AclOrch::~AclOrch()
@@ -825,6 +829,8 @@ AclOrch::~AclOrch()
 
     m_bCollectCounters = false;
     m_sleepGuard.notify_all();
+
+    m_countersThread.join();
 }
 
 void AclOrch::update(SubjectType type, void *cntx)

orchagent/aclorch.h

@@ -3,6 +3,7 @@
 
 #include <iostream>
 #include <sstream>
+#include <thread>
 #include <mutex>
 #include <tuple>
 #include <condition_variable>
@@ -274,6 +275,8 @@ class AclOrch : public Orch, public Observer
 
     PortsOrch *m_portOrch;
     MirrorOrch *m_mirrorOrch;
+
+    thread m_countersThread;
 };
 
 #endif /* SWSS_ACLORCH_H */