[interfaces]: Do not bring up LAG members when LAG is not up (#480)

- Do not bring up LAG member ports when LAG is not created.
  This is because LAG member ports must be DOWN when joining
  the teamd instances due to teamd design. Therefore, we cannot
  bring up a LAG member port first and then join the port to a LAG.

Signed-off-by: Shuotian Cheng <shuche@microsoft.com>

files/image_config/interfaces/interfaces.j2

@@ -76,7 +76,7 @@ auto {{ member }}
 allow-hotplug {{ member }}
 iface {{ member }} inet manual
     pre-up teamdctl {{ pc }} port add {{ member }} || true
-    post-up ifconfig {{ member }} up
+    post-up ip link show {{ pc }} && ifconfig {{ member }} up
     post-down ifconfig {{ member }} down
 #
 {% endfor %}