wil6210: BRP antenna limit API

Added vendor command for setting BRP antenna limit.
It allows user space to set the number of antennas that will be active
in different modes for each connection.

Change-Id: I8a0eb1fa4c74b169faeec2761818a5bac60a8196
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>
Signed-off-by: Lior David <liord@codeaurora.org>