igb: Initialize mailbox message for VF reset

commit de5dc443 upstream.

When a MAC address is not assigned to the VF, that portion of the message
sent to the VF is not set. The memory, however, is allocated from the
stack meaning that information may be leaked to the VM. Initialize the
message buffer to 0 so that no information is passed to the VM in this
case.

Fixes: 6ddbc4cf

 ("igb: Indicate failure on vf reset for empty mac address")
Reported-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20221212190031.3983342-1-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>