iwlwifi: pcie: properly implement NAPI

Instead of pretending to have NAPI and then relying entirely on
interrupts anyway, properly implement NAPI and schedule the poll
when we get an interrupt, re-enabling the interrupt only after
the poll completed.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210117130510.a5951ac4fc06.I9c84a147288fcfb1b019572c6758f2d92949f5d7@changeid
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>