MINOR: spoe: Add "pipelining" and "async" options in spoe-agent section

These options can be used to enable or to disable (prefixing the option line
with the "no" keyword), respectively, pipelined and asynchronous exchanged
between HAproxy and agents. By default, pipelining and async options are
enabled.
diff --git a/include/types/spoe.h b/include/types/spoe.h
index b65bc7a..e8ef7a1 100644
--- a/include/types/spoe.h
+++ b/include/types/spoe.h
@@ -34,6 +34,8 @@
 
 /* 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) */
+#define SPOE_FL_ASYNC             0x00000004 /* Set when SPOE agent supports async (set by default) */
 
 /* Flags set on the SPOE context */
 #define SPOE_CTX_FL_CLI_CONNECTED 0x00000001 /* Set after that on-client-session event was processed */