batctl: Change maintainer to Simon Wunderlich

Marek Lindner forwarded all recent requests regarding the package changes
to Simon. He also asked that further changes should be handled directly
without waiting for him.

Simon Wunderlich already has write access to the repository and is
therefore well prepared to take over the role of the maintainer.

Signed-off-by: Sven Eckelmann <sven@narfation.org>