zebra: use prefix2str for logging where possible

This makes code more robust, consice and readable.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/interface.c b/zebra/interface.c
index 54d8b10..80eb6aa 100644
--- a/zebra/interface.c
+++ b/zebra/interface.c
@@ -1593,10 +1593,9 @@
 	      {
 		char buf[INET6_ADDRSTRLEN];
 		p = ifc->address;
-		vty_out (vty, " ip%s address %s/%d",
+		vty_out (vty, " ip%s address %s",
 			 p->family == AF_INET ? "" : "v6",
-			 inet_ntop (p->family, &p->u.prefix, buf, sizeof(buf)),
-			 p->prefixlen);
+			 prefix2str (p, buf, sizeof(buf)));
 
 		if (ifc->label)
 		  vty_out (vty, " label %s", ifc->label);