[ICMP]: Restore pskb_pull calls in receive function

Somewhere along the development of my ICMP relookup patch the header
length check went AWOL on the non-IPsec path.  This patch restores the
check.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>