* Make kr_{send,recv} report status via return code instaed of errno
 * Move mg_if_* recv and connect callback invocation out of LWIP
   callbacks: these can be nested and we don't want that to happen
   to our callbacks. Instead, we post events for the event manager to
   process during next poll.

PUBLISHED_FROM=9b3c1de796fae381dea1641807e51d7a897a398e