wl1271: Configure a higher listen interval to AP upon association

Increase the fixed listen-interval max value configured to the mac80211 on
driver init. This value will allow a larger value to be configured to the
AP, which means the AP will buffer our frames longer.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>