babeld: address some compilation warnings

Including system headers is not necessary with zebra.h included and
sometimes results in "__ASSERT_FUNCTION redefined" compilation warning.

* babeld.c
  * babel_distribute_update_interface(): make static
* babel_interface.c
  * interface_config_write(): unused 'babel_ifp'
  * don't include system headers
* message.c
  * send_request(): unused 'babel_ifp'
  * send_multihop_request(): idem
  * don't include system headers
* route.c: don't include system headers
* xroute.c: idem
* source.h: newline at EOF
* message.h: idem
diff --git a/babeld/babeld.c b/babeld/babeld.c
index 18b4e34..3dc35b5 100644
--- a/babeld/babeld.c
+++ b/babeld/babeld.c
@@ -560,7 +560,7 @@
     }
 }
 
-void
+static void
 babel_distribute_update_interface (struct interface *ifp)
 {
     struct distribute *dist;