vyos-kernel: enable atheros HTC drivers in the helium 3.13 kernel

The current kernel (3.13) used in the helium branch of VyOS doesn't
include the ath9k_htc kernel modules, preventing the use of these
cards on such a system.  The current hydrogen release has support for
these cards, along with both the old and new firmware maps required.

Bug #266 http://bugzilla.vyos.net/show_bug.cgi?id=266