validate wifi Access Point channel

[anecdata]

Before this PR, a call to start an AP with an invalid channel (not 1-13) would succeed, but the channel would be set to 1, and on espressif, the supplied SSID would be superceded by the default naming, ESP_XXYYZZ.

This PR borrows from the Monitor code and adds the check that the supplied channel is 1-13:

>>> wifi.radio.start_ap(ssid="ssid", password="password", authmode=[wifi.AuthMode.WPA2, wifi.AuthMode.PSK], channel=14)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: channel must be 1-13

[bill88t]

Looks good. Also nice branch name.

[tannewt]

Thank you!