[py-swsssdk]: Update sonic-py-swsssdk submodule (#1048)

Shuotian Cheng · qiluo-msft · commit ee168b0c09e5 · 2017-10-17T14:49:20.000-07:00
Including this commit:
[port_util]: Return empty dictionary instead of a NoneType in get_bridge_port_map

Signed-off-by: Shu0T1an ChenG &lt;shuche@microsoft.com&gt;
diff --git a/src/sonic-py-swsssdk b/src/sonic-py-swsssdk
@@ -1 +1 @@
-Subproject commit 96b4928e790bbce7c959f0b5cbb0510e5954afb1
+Subproject commit a21b7a929ab63f027e4a0d2f919145d8054b8011
