ip6-nd: fix ip6 ra cli issue

Fix parse problem with per-prefix settings (e.g. valid-lifetime)
in ip6 ra.

Type: fix
Signed-off-by: me@hrntknr.net
Change-Id: I2a00bf5b9621ebc16211227d70e376fc2f61bae1

src/vnet/ip6-nd/ip6_ra.c

@@ -2025,8 +2025,7 @@ ip6_ra_cmd (vlib_main_t * vm,
 	}
       else
 	{
-	  error = unformat_parse_error (line_input);
-	  goto done;
+	  break;
 	}
     }