[portsyncd]: Update the MTU on host interfaces if config DB changes (s…

…onic-net#375)

Signed-off-by: Haiyang Zheng <haiyang.z@alibaba-inc.com>

portsyncd/portsyncd.cpp

@@ -13,6 +13,7 @@
 #include "producerstatetable.h"
 #include "portsyncd/linksync.h"
 #include "subscriberstatetable.h"
+#include "exec.h"
 
 #define DEFAULT_PORT_CONFIG_FILE     "port_config.ini"
 
@@ -250,6 +251,19 @@ void handlePortConfig(ProducerStateTable &p, map<string, KeyOpFieldsValuesTuple>
             if (op == SET_COMMAND)
             {
                 p.set(key, values);
+                for (auto fv : values)
+                {
+                    string field = fvField(fv);
+                    string value = fvValue(fv);
+
+                    /* Update the mtu field on host interface */
+                    if (field == "mtu")
+                    {
+                        string cmd, res;
+                        cmd = "ip link set " + key + " mtu " + value;
+                        swss::exec(cmd, res);
+                     }
+                }
             }
 
             it = port_cfg_map.erase(it);