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

The type file is becoming a mess, half of it is for the proxy protocol,
another good part describes conn_streams and mux ops, it would deserve
being split again. At least it was reordered so that elements are easier
to find, with the PP-stuff left at the end. The MAX_SEND_FD macro was moved
to compat.h as it's said to be the value for Linux.
diff --git a/src/listener.c b/src/listener.c
index 4d1d2de..6a13b1c 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -20,6 +20,7 @@
 
 #include <haproxy/api.h>
 #include <common/cfgparse.h>
+#include <haproxy/connection.h>
 #include <haproxy/errors.h>
 #include <haproxy/global.h>
 #include <haproxy/list.h>
@@ -31,7 +32,6 @@
 #include <haproxy/protocol-t.h>
 
 #include <proto/acl.h>
-#include <proto/connection.h>
 #include <haproxy/fd.h>
 #include <haproxy/freq_ctr.h>
 #include <proto/log.h>