scsi: be2iscsi: Fix gateway APIs to support IPv4 & IPv6

Gateway APIs assume IP type as IPv4. Modify it to be generic to allow
clearing of IPv6 gateway set using BIOS.

Signed-off-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>