Robustness fixes (and some callback invocation) by Luke Howard.

Robustness fixes (and some callback invocation) by Luke Howard.

* lib/packet.c (_packet_create): Set packet identity properly.
(_do_send): Return an int.
(_do_send): Don't ignore rad_encode() errors.
(_do_send): Do invoke rad_sign().
(_event_cb): Invoke callbacks.
(_event_cb): Honour _do_send() return code.
(_read_cb): Check packet (by invoking rad_packet_ok()).
(_read_cb): Don't ignore rad_decode() errors.
(_read_cb): Invoke callbacks.