MINOR: log: make MAX_SYSLOG_LEN overridable at build time

This value was set in log.h without any #ifndef around, so when one
wanted to change it, a patch was needed. Let's move it to defaults.h
with the usual #ifndef so that it's easier to change it.

include/common/defaults.h

@@ -48,6 +48,10 @@
 #define CAPTURE_LEN     64
 #endif
 
+#ifndef MAX_SYSLOG_LEN
+#define MAX_SYSLOG_LEN          1024
+#endif
+
 // maximum line size when parsing config
 #ifndef LINESIZE
 #define LINESIZE	2048

include/types/log.h

@@ -28,7 +28,6 @@
 #include <common/config.h>
 #include <common/mini-clist.h>
 
-#define MAX_SYSLOG_LEN          1024
 #define NB_LOG_FACILITIES       24
 #define NB_LOG_LEVELS           8
 #define SYSLOG_PORT             514