nl80211: Restore previous nlmode if set_freq for AP mode fails

nl80211: Restore previous nlmode if set_freq for AP mode fails

wpa_driver_nl80211_ap() returned error if set_freq failed, but left the
previously set nlmode to GO/AP. While this should not be issue for most
purposes, it leaves the interface in somewhat unexpected state and could
potentially affect operations prior to next connection attempt. Address
this by restoring the previous nlmode if AP mode cannot be started for
some reason.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>