[CLEANUP] remove many #include <types/xxx> from C files

It should be stated as a rule that a C file should never
include types/xxx.h when proto/xxx.h exists, as it gives
less exposure to declaration conflicts (one of which was
caught and fixed here) and it complicates the file headers
for nothing.

Only types/global.h, types/capture.h and types/polling.h
have been found to be valid includes from C files.
diff --git a/src/log.c b/src/log.c
index d08ad16..fc04232 100644
--- a/src/log.c
+++ b/src/log.c
@@ -26,10 +26,9 @@
 #include <common/standard.h>
 #include <common/time.h>
 
-#include <types/backend.h>
 #include <types/global.h>
-#include <types/log.h>
-#include <types/session.h>
+
+#include <proto/log.h>
 
 #ifndef MSG_NOSIGNAL
 #define MSG_NOSIGNAL	(0)