... proceed to ipv4_input()


ipv4_input does lots of magic, let us just look at the major points
validate packet, incl checksumming etc
let pf do its work by calling pf_test()
check for multicast
check for ipsec and stuff
figure out wether the packet is for us
if not, check wether we want to forward it, and if so, call ip_forward()
otherwise, proceed with local delivery or drop