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.

src/haproxy.c

@@ -85,6 +85,7 @@
 #include <haproxy/base64.h>
 #include <common/cfgparse.h>
 #include <haproxy/chunk.h>
+#include <haproxy/connection.h>
 #include <haproxy/dns.h>
 #include <haproxy/dynbuf.h>
 #include <haproxy/errors.h>
@@ -122,7 +123,6 @@
 #include <proto/backend.h>
 #include <proto/channel.h>
 #include <proto/cli.h>
-#include <proto/connection.h>
 #include <haproxy/fd.h>
 #include <proto/filters.h>
 #include <proto/log.h>