BUILD: server-state: include tools.h from server_state.c

Many functions from tools.h are called there without the file being
included.
diff --git a/src/server_state.c b/src/server_state.c
index 7235305..6f42a39 100644
--- a/src/server_state.c
+++ b/src/server_state.c
@@ -27,6 +27,7 @@
 #include <haproxy/resolvers.h>
 #include <haproxy/server.h>
 #include <haproxy/ssl_sock.h>
+#include <haproxy/tools.h>
 
 
 /* Update a server state using the parameters available in the params list.