Update error message on old unsupported kernels

Update error message on old unsupported kernels

compat-wireless-2.6-old is deprecated as we can now use
compat-wireless itself but we just need to work extending
support for older kernels. It will also soon be possible
for users to enable older kernels by just selecting
one driver to compile.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>