cfg80211: Remove default dynamic PS timeout value

Now that the mac80211 is choosing dynamic ps timeouts based on the ps-qos
network latency configuration, configure a default value of -1 as the dynamic
ps timeout in cfg80211. This value allows the mac80211 to determine the value
to be used.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>