wil6210: add support for channel 4

wil6210 supports channels 1-3 of the 60GHz band.
New FW added support for channel 4. Add support for channel 4 also in
wil6210 driver.

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>