luci-mod-network: wireless.js: rename `multicast_to_unicast` option

The `multicast_to_unicast` option has been renamed to
`multicast_to_unicast_all` in OpenWrt commit
https://github.com/openwrt/openwrt/commit/09ea1db93

Fixes: #6472
Signed-off-by: Jo-Philipp Wich <jo@mein.io>