MINOR: spoe: Add a type to qualify the message list during encoding

Because we can have messages chained by event or by group, we need to have a way
to know which kind of list we manipulate during the encoding. So 2 types of list
has been added, SPOE_MSGS_BY_EVENT and SPOE_MSGS_BY_GROUP. And the right type is
passed when spoe_encode_messages is called.
diff --git a/include/types/spoe.h b/include/types/spoe.h
index ff649fa..2bfd159 100644
--- a/include/types/spoe.h
+++ b/include/types/spoe.h
@@ -32,6 +32,10 @@
 #include <types/stream.h>
 #include <types/task.h>
 
+/* Type of list of messages */
+#define SPOE_MSGS_BY_EVENT 0x01
+#define SPOE_MSGS_BY_GROUP 0x02
+
 /* Flags set on the SPOE agent */
 #define SPOE_FL_CONT_ON_ERR       0x00000001 /* Do not stop events processing when an error occurred */
 #define SPOE_FL_PIPELINING        0x00000002 /* Set when SPOE agent supports pipelining (set by default) */