iwlwifi: mvm: BT Coex - always set mandatory fields

The firmware always expects the Coex Mode to be set.
Moreover, the firmware expects bit 0 is the valid bits to
be set all the times.
I misunderstood the API and didn't set these bits when
commands are sent to update the paramters of the Coex. As
a result, the firmware understood that the BT Coex was
disabled (Coex mode = 0) and ignored all the updates (valid
bit 0 clear).

Fix that.

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