nl80211: Initialize full channel info struct even if channel is not known

nl80211: Initialize full channel info struct even if channel is not known

It was possible for the driver to advertise support for channels that
are not found from wpa_supplicant frequency-to-channel mapping (e.g.,
channel 182 at 5910 MHz) and that resulted in not initializing the
channel number information. Fix this by explicitly clearing the full
struct hostapd_channel_data buffer before parsing the information into
it from the driver.

This avoids some conditional jumps that could have dependent on
uninitialized values.

Signed-off-by: Jouni Malinen <j@w1.fi>