iwlwifi: mvm: fix fw monitor 7000 HW recollecting

To stop and start the FW monitor in the 7000 HW
family we need to use a different bit, otherwise
after stopping it for the first time - it won't
get restarted. Use the correct bitmask.

Note: This fix is only for DRAM collection mode.
      For other modes, an additional fix will be
      needed.

Signed-off-by: Liad Kaufman <liad.kaufman@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>