iwlwifi: pcie: track interrupt mask in SW

Track the interrupt mask in software, making it exactly
what is configured in the interrupt mask register in the
hardware.
This allows not to access the register from the interrupt
handler. This was the case for ICT interrupt already, but
not for non-ICT interrupt.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>