bgpd, lib: adopt afi_t and safi_t in several places

* bgpd/bgp_attr.c, bgpd/bgp_open.h, bgpd/bgp_route.c, lib/prefix.c,
  lib/prefix.h: Various integer types were being used where, if we
  had strict type checking, afi_t and safi_t would be required.

Signed-off-by: G.Balaji <balajig81@gmail.com>
(cherry picked from commit c8af35ffa2dc79ff7d7ff00b1b61f1f50a100ab6)
diff --git a/lib/prefix.h b/lib/prefix.h
index a7598b7..5f1ff05 100644
--- a/lib/prefix.h
+++ b/lib/prefix.h
@@ -144,8 +144,8 @@
 }
 
 /* Prototypes. */
-extern int afi2family (int);
-extern int family2afi (int);
+extern int afi2family (afi_t);
+extern afi_t family2afi (int);
 
 extern struct prefix *prefix_new (void);
 extern void prefix_free (struct prefix *);