api: binary api cleanup

api: binary api cleanup

Multiple API message handlers call vnet_get_sup_hw_interface(...)
without checking the inbound sw_if_index. This can cause a
pool_elt_at_index ASSERT in a debug image, and major disorder in a
production image.

Given that a number of places are coded as follows, add an
"api_visible_or_null" variant of vnet_get_sup_hw_interface, which
returns NULL given an invalid sw_if_index, or a hidden sw interface:

-  hw = vnet_get_sup_hw_interface (vnm, sw_if_index);
+  hw = vnet_get_sup_hw_interface_api_visible_or_null (vnm, sw_if_index);
   if (hw == NULL || memif_device_class.index != hw->dev_class_index)
     return clib_error_return (0, "not a memif interface");

Rename two existing xxx_safe functions -> xxx_or_null to make it
obvious what they return.

Type: fix

Change-Id: I29996e8d0768fd9e0c5495bd91ff8bedcf2c5697
Signed-off-by: Dave Barach <dave@barachs.net>