luci-mod-network: Support for disabling routes

luci-mod-network: Support for disabling routes

Support for disabling routes in netifd was added in commit [1]. This commit
adds support for disabling routes through the LuCI interface.

Additionally hidden the route options descriptions in the header of the
routes table (they are still available in the modal view).

[1]: https://git.openwrt.org/?p=project/netifd.git;a=commit;h=327da9895327bc56b23413ee91a6e6b6e0e4329d

Signed-off-by: Anton Kikin <a.kikin@tano-systems.com>
(cherry picked from commit bfe8a01040c8a74f38818195620f069f5bc10c5c)