wil6210: update WIL_MCS_MAX to 15

Update max MCS to 15, which is supported by Talyn-MB.
This will allow collecting statistics on number of RX packets
in higher MCS.

Change-Id: I36e373492725b82c56cddb7853e2c3363e059cbd
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Git-commit: 044974fbeadee4a5c0554ee7d83d22495ad3d450
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


Signed-off-by: Maya Erez <merez@codeaurora.org>