[Mellanox] Fix the memory leak in mlnx-sfpd (sonic-net#3128)

* fix the memory leak in on_pmpe. objects created via sx_api having convention new_<type_name> should be release explicitly via delete_<type_name>.

* avoid duplicate code.

platform/mellanox/mlnx-sfpd/scripts/mlnx-sfpd

@@ -205,36 +205,40 @@ class MlnxSfpd:
         pkt = new_uint8_t_arr(pkt_size)
         recv_info_p = new_sx_receive_info_t_p()
         pmpe_t = sx_event_pmpe_t()
-        logical_port_list = new_sx_port_log_id_t_arr(4)
         port_attributes_list = new_sx_port_attributes_t_arr(64)
         port_cnt_p = new_uint32_t_p()
         uint32_t_p_assign(port_cnt_p,64)
         label_port_list = []
-        status = True
         module_state = 0
 
         rc = sx_lib_host_ifc_recv(fd_p, pkt, pkt_size_p, recv_info_p)
         if rc != 0:
             log_error("sx_lib_host_ifc_recv exited with error, rc %d" % rc)
             status = False
-            return status, label_port_list, module_state
-
-        pmpe_t = recv_info_p.event_info.pmpe
-        port_list_size = pmpe_t.list_size
-        logical_port_list = pmpe_t.log_port_list
-        module_state = pmpe_t.module_state
-
-        for i in xrange(port_list_size):
-            logical_port = sx_port_log_id_t_arr_getitem(logical_port_list, i)
-            rc = sx_api_port_device_get(self.handle, 1 , 0, port_attributes_list,  port_cnt_p)
-            port_cnt = uint32_t_p_value(port_cnt_p)
-
-            for i in xrange(port_cnt):
-                port_attributes = sx_port_attributes_t_arr_getitem(port_attributes_list,i)
-                if port_attributes.log_port == logical_port:
-                    lable_port = port_attributes.port_mapping.module_port
-                    break
-            label_port_list.append(lable_port)
+        else:
+            status = True
+            pmpe_t = recv_info_p.event_info.pmpe
+            port_list_size = pmpe_t.list_size
+            logical_port_list = pmpe_t.log_port_list
+            module_state = pmpe_t.module_state
+
+            for i in xrange(port_list_size):
+                logical_port = sx_port_log_id_t_arr_getitem(logical_port_list, i)
+                rc = sx_api_port_device_get(self.handle, 1 , 0, port_attributes_list,  port_cnt_p)
+                port_cnt = uint32_t_p_value(port_cnt_p)
+
+                for i in xrange(port_cnt):
+                    port_attributes = sx_port_attributes_t_arr_getitem(port_attributes_list,i)
+                    if port_attributes.log_port == logical_port:
+                        lable_port = port_attributes.port_mapping.module_port
+                        break
+                label_port_list.append(lable_port)
+
+        delete_uint32_t_p(pkt_size_p)
+        delete_uint8_t_arr(pkt)
+        delete_sx_receive_info_t_p(recv_info_p)
+        delete_sx_port_attributes_t_arr(port_attributes_list)
+        delete_uint32_t_p(port_cnt_p)
 
         return status, label_port_list, module_state,