netxen: build fix for INET=n

When CONFIG_INET is disabled, netxen has a build failure:

netxen_nic_main.c:(.text+0x118fd1): undefined reference to `netxen_config_indev_addr'

so make that function just an empty stub when CONFIG_INET=n.
(not "inline" since that conflicts with other declarations of it)

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