BUILD: connection: include tools.h in connection.c

Several functions from tools.h are called there without the file being
included.
diff --git a/src/connection.c b/src/connection.c
index 67b2124..3e3fb00 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -25,6 +25,7 @@
 #include <haproxy/sample.h>
 #include <haproxy/ssl_sock.h>
 #include <haproxy/stream_interface.h>
+#include <haproxy/tools.h>
 
 
 DECLARE_POOL(pool_head_connection,     "connection",     sizeof(struct connection));