igb: Avoid uninitialized advertised variable in eee_set_cur

eee_get_cur assumes that the output data is already zeroed. It can
read-modify-write the advertised field:

              if (ipcnfg & E1000_IPCNFG_EEE_100M_AN)
2594			edata->advertised |= ADVERTISED_100baseT_Full;

This is ok for the normal ethtool eee_get call, which always
zeroes the input data before.

But eee_set_cur also calls eee_get_cur and it did not zero the input
field. Later on it then compares agsinst the field, which can contain partial
stack garbage.

Zero the input field in eee_set_cur() too.

Cc: jeffrey.t.kirsher@intel.com
Cc: netdev@vger.kernel.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>