BUG/MEDIUM: contrib/spoa-server: Fix ipv4_address used instead of ipv6_address

Typo leads to checking the wrong object for memory issues

This patch must be backported as far as 2.0.
diff --git a/contrib/spoa_server/ps_python.c b/contrib/spoa_server/ps_python.c
index 6843cdc..5cb7ca8 100644
--- a/contrib/spoa_server/ps_python.c
+++ b/contrib/spoa_server/ps_python.c
@@ -415,7 +415,7 @@
 	}
 
 	ipv6_address = PyObject_GetAttrString(module_ipaddress, "IPv6Address");
-	if (ipv4_address == NULL) {
+	if (ipv6_address == NULL) {
 		PyErr_Print();
 		return 0;
 	}