[IPV4] raw: Strengthen check on validity of iph->ihl
We currently check that iph->ihl is bounded by the real length and that
the real length is greater than the minimum IP header length. However,
we did not check the caes where iph->ihl is less than the minimum IP
header length.
This breaks because some ip_fast_csum implementations assume that which
is quite reasonable.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>