batctl: Enable build of mcast_flags subcommand

batctl: Enable build of mcast_flags subcommand

The mcast_flags subcommand allows to query the mcast_flags of the current
device and of the seen originators. It should be enabled for the default
and full variants. But the configuration string wasn't correctly included
in the list when the variants were prepared and thus disabled in all
variants.

Reported-by: Linus Lüssing <linus.luessing@c0d3.blue>
Fixes: 129986825219 ("batctl: Provide different variants")
Signed-off-by: Sven Eckelmann <sven@narfation.org>