kernel/802_11: Fix panic when the desired ratectl algorithm is unavailable.

kernel/802_11: Fix panic when the desired ratectl algorithm is unavailable.

Set the default to NONE. When a driver calls ieee80211_ratectl_init(), try
to use AMRR etc. if NONE is selected. Drivers may still select other
algorithms using ieee80211_ratectl_set() prior to calling _init().

Due to our broken ieee80211_load_module(), we do not currently autoload
the desired ratectl algorithm like FreeBSD does. Instead, a message about
manually loading the module will be printed (see ieee80211_dragonfly.c).

Reported-by: profmakx
Taken-from:  FreeBSD