bgpd: add flag checks for MP_(UN)REACH_NLRI

* bgp_attr.[ch]
  * bgp_mp_reach_parse(): add extra arguments and a uniform flag
    check block
  * bgp_mp_unreach_parse(): idem
  * bgp_attr_parse(): provide extra arguments
* bgp_mp_attr_test.c
  * parse_test(): justify respective calls
diff --git a/bgpd/bgp_attr.h b/bgpd/bgp_attr.h
index c011251..e630074 100644
--- a/bgpd/bgp_attr.h
+++ b/bgpd/bgp_attr.h
@@ -180,8 +180,9 @@
 void transit_unintern (struct transit *);
 
 /* Exported for unit-test purposes only */
-extern int bgp_mp_reach_parse (struct peer *, bgp_size_t, struct attr *,
-			       struct bgp_nlri *);
-extern int bgp_mp_unreach_parse (struct peer *, bgp_size_t, struct bgp_nlri *);
+extern int bgp_mp_reach_parse (struct peer *, const bgp_size_t, struct attr *,
+			       const u_char, u_char *, struct bgp_nlri *);
+extern int bgp_mp_unreach_parse (struct peer *, const bgp_size_t, const u_char,
+                                 u_char *, struct bgp_nlri *);
 
 #endif /* _QUAGGA_BGP_ATTR_H */