zebra: use prototypes/includes in rt_netlink

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/rtread_netlink.c b/zebra/rtread_netlink.c
index 066e844..7abbc59 100644
--- a/zebra/rtread_netlink.c
+++ b/zebra/rtread_netlink.c
@@ -23,8 +23,7 @@
 #include <zebra.h>
 
 #include "zebra/zserv.h"
-
-extern void netlink_route_read (void);
+#include "rt_netlink.h"
 
 void route_read (void)
 {