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/bgpd/bgp_snmp.c b/bgpd/bgp_snmp.c
index 662186b..c4490bf 100644
--- a/bgpd/bgp_snmp.c
+++ b/bgpd/bgp_snmp.c
@@ -30,6 +30,7 @@
 #include "command.h"
 #include "thread.h"
 #include "smux.h"
+#include "filter.h"
 
 #include "bgpd/bgpd.h"
 #include "bgpd/bgp_table.h"