lib, bgpd: Remove 'struct fifo' from lib/zebra.h

The 'struct fifo' and it's accompanying #defines do not
belong in lib/zebra.h.  Move them into their own header.

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/bgpd/bgp_advertise.h b/bgpd/bgp_advertise.h
index adbbe30..51ba626 100644
--- a/bgpd/bgp_advertise.h
+++ b/bgpd/bgp_advertise.h
@@ -21,6 +21,8 @@
 #ifndef _QUAGGA_BGP_ADVERTISE_H
 #define _QUAGGA_BGP_ADVERTISE_H
 
+#include <lib/fifo.h>
+
 /* BGP advertise attribute.  */
 struct bgp_advertise_attr
 {