Unlike /proc/sys/net/ipv4/conf/INTF/rp_filter flag, rule iptables -t raw
-I PREROUTING -m rpfilter --invert -j DROP prevents conntrack table to
become full when a packet flood with randomly selected source IP addresses
is received from the lan side.
Signed-off-by: Alin Nastac <alin.nastac@gmail.com>