nl80211: Increase buffer size for reporting scan frequencies

nl80211: Increase buffer size for reporting scan frequencies

It is possible for a driver to support sufficient number of channels to
hit the previous limit of 200 characters for the "nl80211: Scan included
frequencies:" debug message. Increase the maximum buffer length to 300
characters to allow more complete list of scanned frequencies to be
written into the debug log. This limit is more in line with the
MAX_REPORT_FREQS (50) limit.

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