Commit a temporary workaround for people who are building kernels
where they've disabled all the wireless devices/framework.

This is just a build workaround. If you're actively using wireless,
you must still define AH_SUPPORT_AR5416 as I'm not sure what else
will break!

The real solution is to make the module build depend if AH_SUPPORT_AR5416
is defined, as well as make the 11n code in if_ath_tx.c and if_ath_tx_ht.c
completely optional (maybe depend upon ATH_SUPPORT_11N.)