batctl: add new package

batctl: add new package

batctl is the user space configuration and debugging tool for
the B.A.T.M.A.N. Advanced kernel module. It is packaged in three
variants (tiny, default, full) with different sets of subcommands.

Moved from the openwrt/routing feed, as discussed in
https://github.com/openwrt/routing/issues/184.

The one deviation from the feed copy is SUBMENU:=Wireless, which the
feed copy does not set at all: without it the three variants sit
ungrouped at the top of the Network menu. Wireless keeps them next to
mesh11sd and alfred, which move across with the same value. A dedicated
Mesh submenu is the better home for all three and is worth adding once
enough of the mesh packages have landed to justify it.

Signed-off-by: Josef Schlehofer <redacted>
Co-authored-by: Claude Fable 5 <redacted>