[global] drop usage of recvmmsg inside libknet

as requested by different kernel developers, we should stop
using both sendmmsg and recvmmsg.

as temporary solution use Jan's compat wrappers. the whole TX/RX
code will need review to do a full proper switch since all
error codes will change and propagate differently to transport hooks
and knet_send_sync users

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