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/bgpd/bgp_open.h b/bgpd/bgp_open.h
index 59265dc..2b1382d 100644
--- a/bgpd/bgp_open.h
+++ b/bgpd/bgp_open.h
@@ -31,9 +31,9 @@
 /* Generic MP capability data */
 struct capability_mp_data
 {
-  u_int16_t afi;
+  afi_t afi;
   u_char reserved;
-  u_char safi;
+  safi_t safi;
 };
 
 #pragma pack(1)
@@ -55,8 +55,8 @@
 
 struct graceful_restart_af
 {
-  u_int16_t afi;
-  u_char safi;
+  afi_t afi;
+  safi_t safi;
   u_char flag;
 };