These were added to the `network` module but not the `network.WLAN` class,
which is the new home for such constants.
Also:
- Mark the WLAN constants in the `network` module as deprecated, to be
removed in MicroPython 2.0.
- Move the static assert to the WLAN source code, to be close to where it
relates to.
Signed-off-by: Damien George <damien@micropython.org>