iwlwifi: make hw crypto context aware

HW crypto needs to be aware of the context, and there
are different command IDs for the WEP keys per context,
so move the key tracking variables and command IDs into
the context structure.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>