[ospfd/BSD] add missing UINT16_MAX - picked up from FreeBSD ports patch

Should probably have AC_TYPE_UINT16_T in configure.ac to make it really
clean...  and a fresh import of gnulib, the existing copy of gnulib seems to
be manually put some stuff in zebra.h.  I'm leaving that alone for now,
since a fresh import will probably clean up a lot of cruft and it would be a
duplicated effort to fix some things now.

The FreeBSD port 0.99.11_1 files/patch-ospfd-ospfd.h can probably go away
after this is applied.
diff --git a/ospfd/ospfd.h b/ospfd/ospfd.h
index 6ba1916..f81c682 100644
--- a/ospfd/ospfd.h
+++ b/ospfd/ospfd.h
@@ -23,6 +23,8 @@
 #ifndef _ZEBRA_OSPFD_H
 #define _ZEBRA_OSPFD_H
 
+#include <zebra.h>
+
 #include "filter.h"
 #include "log.h"