cnic, bnx2: Check iSCSI support early in bnx2_init_one()

Based on earlier patch from Neil Horman <nhorman@tuxdriver.com>

If iSCSI is not supported on a bnx2 device, bnx2_cnic_probe() will
return NULL and the cnic device will not be visible to bnx2i.  This
will prevent bnx2i from registering and then unregistering during
cnic_start() and cause the warning message:

bnx2 0003:01:00.1: eth1: Failed waiting for ULP up call to complete

Signed-off-by: Michael Chan <mchan@broadcom.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>