bgpd, lib: adopt afi_t and safi_t in several places

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)