iwlwifi: add iwl_set_bits_mask to transport API

Express iwl_set_bit() and iwl_clear_bit() through iwl_set_bits_mask()
and add the latter to the transport's API in order to allow different
implementation for different transport types in the future.

Signed-off-by: Lilach Edelstein <lilach.edelstein@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>