Staging: sxg: Add multicast support for Sahara SXG driver

* Add multicast support for SXG driver for Alacritech's 10Gbe products.

Signed-off-by: LinSysSoft Sahara Team <saharaproj@linsyssoft.com>
Signed-off-by: Mithlesh Thukral <mithlesh@linsyssoft.com>
Cc: Michael Miles <mmiles@alacritech.com>
Cc: Christopher Harrer <charrer@alacritech.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>