iwlwifi: add a mechanism to disable plcp error checking

For some devices, especially the upcoming new devices, the plcp error
rate is different. Before the correct error rate can be determine, also
for the debugging purpose; add the mechanism to disable plcp error checking
which cause radio reset happen.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>