ath11k: add handling for BSS color

This patch adds code to handle the BSS_CHANGED_BSS_COLOR flag. It will
trigger the propagation of BSS color settings into the FW. Handling is
slightly different between AP and STA interfaces.

Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>