wil6210: Add support for setting RBUFCAP configuration

RBUFCAP support added in FW.
The RBUFCAP feature is amendment to the block ack mechanism to
prevent overloading of the recipient’s memory space, which may
happen in case the link speed is higher than STA’s capability
to process or consume incoming data.
The block ack policy (ba_policy) is now controlled by FW so driver
should ignore this field.
Add new debugfs "rbufcap" to configure RBUFCAP.

Change-Id: Id3b83c607c8b4d61926718862cdf4f4931303e38
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>
Git-commit: c5b3a6582b1e9fad0fb0b8658855387c0cbcc576
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


[merez@codeaurora.org: trivial merge conflicts]
Signed-off-by: Maya Erez <merez@codeaurora.org>