hostapd: Fix opclass during CSA with DFS channels

hostapd: Fix opclass during CSA with DFS channels

During CSA with DFS channels, disable, enable interface is a part of the
algorithm. When interface was enabled old operating class before switch
and new channel were used causing mismatch in
configured_fixed_chan_to_freq() function.

Example of log when switch from channel 157 to 108 was triggered:
"Could not convert op_class 124 channel 108 to operating frequency"

Fixes: bb781c763 ("AP: Populate iface->freq before starting AP")
Signed-off-by: Marek Kwaczynski <marek@mazekey.pl>