igb: fix bit_shift to be in [1..8] range

[ Upstream commit 60d75865 ]

In igb_hash_mc_addr() the expression:
        "mc_addr[4] >> 8 - bit_shift", right shifting "mc_addr[4]"
shift by more than 7 bits always yields zero, so hash becomes not so different.
Add initialization with bit_shift = 1 and add a loop condition to ensure
bit_shift will be always in [1..8] range.

Fixes: 9d5c8243 ("igb: PCI-Express 82575 Gigabit Ethernet driver")
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>