luci-mod-network: adapt to current 802.11r defaults

luci-mod-network: adapt to current 802.11r defaults

The default for 802.11r option ft_psk_generate_local
was changed a few months ago by openwrt/openwrt@3cc56a5

That change was a bit awkward, as it made hostapd to
overlook the possibly existing r0kh values by default
unless the user explicitly disables the new default.

Adapt LuCI by changing the default for ft_psk_generate_local
into 'enabled'.

But ensure that LuCI does not delete the existing key values
by not making the r0kh and r1kh fields to depend on this.

Note that this is just a quick fix for the wrong default value
causing problems, but not yet a complete fix for all the options.
In the long run it might be better to make the detail options
to depend on local generation.

Reference also to LuCI PR #2102

Adapted from commit 26e903c74 in master

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>