[NETFILTER]: iptable_raw: ignore short packets sent by SOCK_RAW sockets

iptables matches and targets expect packets to have at least a full
IP header and a valid header length. Ignore packets sent through
raw sockets for which this isn't true as in the other tables.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>