iwlwifi: add default WEP key host command

This patch adds declaration for static WEP host command. This command will
be used for default WEP group keys when no key mapping keys are used.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>