libknet: implement basic ring buffer for bcast packets

fix KNET_FRAME_SIZE handling around

don't try to send messages to links that are not ready

gather host info for all incoming pkcts (data/ping) since there
is no point to go crazy figuring it out

add basic ring buffer functions based on playground implementation
(still missing reset of the buffer)

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>