wil6210: add support for set_cqm_rssi_config

set_cqm_rssi_config() is used by the kernel to configure connection
quality monitor RSSI threshold.
wil6210 uses WMI_SET_LINK_MONITOR_CMDID to set the RSSI threshold to
FW which in turn reports RSSI threshold changes with
WMI_LINK_MONITOR_EVENTID.

Signed-off-by: Dedy Lansky <dlansky@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>