wil6210: set default 3-MSI

Single MSI is the current default configuration.
With multiple MSI interrupts configuration, Tx/Rx processing could
run in parallel on different CPU cores and allow better balance
between the cores.

Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>