wcn36xx: switch on antenna diversity feature bit

The official feature-complete WCN3680B driver (known as prima, open source
but not upstream) sends this feature bit.

As we wish to support the antenna diversity feature in upstream, we need
to set this bit as well.

Signed-off-by: Benjamin Li <benl@squareup.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211025175359.3591048-2-benl@squareup.com