[vstest]: fix test_port_an_warm.py test (sonic-net#779)

the test should set the speed and autoneg in config db instead
of application db. As if the speed in config db is not changed,
it will override the value in app db after warm reboot

Signed-off-by: Guohan Lu <gulv@microsoft.com>

Author: lguohan

tests/test_port_an_warm.py

@@ -12,9 +12,9 @@ def test_PortAutoNeg_warm(dvs, testlog):
     ctbl = swsscommon.Table(cdb, "PORT")
     stbl = swsscommon.Table(sdb, "PORT_TABLE")
 
-    # set autoneg = false and speed = 1000
+    # set autoneg = true and speed = 1000
     fvs = swsscommon.FieldValuePairs([("autoneg","1"), ("speed", "1000")])
-    tbl.set("Ethernet0", fvs)
+    ctbl.set("Ethernet0", fvs)
 
     time.sleep(1)
 
@@ -35,7 +35,7 @@ def test_PortAutoNeg_warm(dvs, testlog):
     # set speed = 100
     fvs = swsscommon.FieldValuePairs([("speed", "100")])
 
-    tbl.set("Ethernet0", fvs)
+    ctbl.set("Ethernet0", fvs)
 
     time.sleep(1)