net: hsr: Add support for MC filtering at the slave device

When MC (multicast) list is updated by the networking layer due to a
user command and as well as when allmulti flag is set, it needs to be
passed to the enslaved Ethernet devices. This patch allows this
to happen by implementing ndo_change_rx_flags() and ndo_set_rx_mode()
API calls that in turns pass it to the slave devices using
existing API calls.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Ravi Gunasekaran <r-gunasekaran@ti.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>