REORG: include: move pipe.h to haproxy/pipe{,-t}.h

No change was needed beyond a minor cleanup.
diff --git a/src/pipe.c b/src/pipe.c
index 6fe7b05..992c77b 100644
--- a/src/pipe.c
+++ b/src/pipe.c
@@ -18,7 +18,7 @@
 #include <haproxy/pool.h>
 
 #include <types/global.h>
-#include <types/pipe.h>
+#include <haproxy/pipe-t.h>
 
 DECLARE_STATIC_POOL(pool_head_pipe, "pipe", sizeof(struct pipe));