iwlwifi: correctly set the NMI register

When we want to trigger an NMI in the device, we need to set
bit 7 and not bit 0. However, older firmwares don't register
to the interrupt issued by bit 7. Use bit 7 first so that
the correct interrupt will be issued hoping that the firmware
will react. To be on the safe side, set bit 0 in case the
firmware didn't register to the proper interrupt.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>