lib, bgpd, tests: Refactor FILTER_X in zebra.h

lib/zebra.h has FILTER_X #define's.  These do not belong there.
Put them in lib/filter.h where they belong.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/lib/filter.h b/lib/filter.h
index 37535cb..e6ccd33 100644
--- a/lib/filter.h
+++ b/lib/filter.h
@@ -25,6 +25,11 @@
 
 #include "if.h"
 
+/* Filter direction.  */
+#define FILTER_IN                 0
+#define FILTER_OUT                1
+#define FILTER_MAX                2
+
 /* Filter type is made by `permit', `deny' and `dynamic'. */
 enum filter_type 
 {