wifi: ignore disabled frequencies
Frequencies with the 'disabled' flag are supported by the driver but disabled in the current regulatory domain. Don't add them to the list of supported frequencies since they are not usable; this is needed especially in AP mode, where NM chooses a random frequency among the supported ones.
Disabled channels are displayed in the 'iw' output as '(disabled):
[...]
Frequencies:
* 2412 MHz [1] (30.0 dBm)
* 2417 MHz [2] (30.0 dBm)
* 2422 MHz [3] (30.0 dBm)
* 2427 MHz [4] (30.0 dBm)
* 2432 MHz [5] (30.0 dBm)
* 2437 MHz [6] (30.0 dBm)
* 2442 MHz [7] (30.0 dBm)
* 2447 MHz [8] (30.0 dBm)
* 2452 MHz [9] (30.0 dBm)
* 2457 MHz [10] (30.0 dBm)
* 2462 MHz [11] (30.0 dBm)
* 2467 MHz [12] (disabled)
* 2472 MHz [13] (disabled)
* 2484 MHz [14] (disabled)
Note that currently NM loads the list only at startup and therefore, in case of a change of regulatory domain, a restart of the daemon is needed to have the list updated. This needs to be improved.