[MINOR] move error codes to common/errors.h
It's useful to be able to share error codes between C files,
so move the codes currently only used in protocols to a generic
file.
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index 24c435f..307d7ef 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -28,6 +28,7 @@
#include <common/compat.h>
#include <common/config.h>
#include <common/debug.h>
+#include <common/errors.h>
#include <common/memory.h>
#include <common/mini-clist.h>
#include <common/standard.h>