[teammgrd]: Add kernel master check for port before enslaving (#681)

Check if the port is already enslaved, and prevent extra movement
that triggers a link flap when adding the port into the port channel.

Signed-off-by: Shu0T1an ChenG <shuche@microsoft.com>

cfgmgr/teammgr.cpp

@@ -11,8 +11,9 @@
 #include <sstream>
 #include <thread>
 
-#include <sys/ioctl.h>
 #include <net/if.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
 
 using namespace std;
 using namespace swss;
@@ -237,6 +238,16 @@ bool TeamMgr::checkPortIffUp(const string &port)
     return ifr.ifr_flags & IFF_UP;
 }
 
+bool TeamMgr::isPortEnslaved(const string &port)
+{
+    SWSS_LOG_ENTER();
+
+    struct stat buf;
+    string path = "/sys/class/net/" + port + "/master";
+
+    return lstat(path.c_str(), &buf) == 0;
+}
+
 bool TeamMgr::findPortMaster(string &master, const string &port)
 {
     SWSS_LOG_ENTER();
@@ -280,7 +291,7 @@ void TeamMgr::doPortUpdateTask(Consumer &consumer)
             SWSS_LOG_INFO("Received port %s state update", alias.c_str());
 
             string lag;
-            if (findPortMaster(lag, alias))
+            if (!isPortEnslaved(alias) && findPortMaster(lag, alias))
             {
                 if (addLagMember(lag, alias) == task_need_retry)
                 {

cfgmgr/teammgr.h

@@ -46,6 +46,7 @@ class TeamMgr : public Orch
     bool setLagAdminStatus(const string &alias, const string &admin_status);
     bool setLagMtu(const string &alias, const string &mtu);
 
+    bool isPortEnslaved(const string &);
     bool findPortMaster(string &, const string &);
     bool checkPortIffUp(const string &);
     bool isPortStateOk(const string&);