netxen: fix CONFIG_INET=n build

Wrap dest IP hashing code with #ifdef CONFIG_INET,
this feature makes no sense without INET, but other
driver can still work.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>