MAINTAINERS: make Breno the netconsole maintainer

netconsole has no maintainer, and Breno has been working on
improving it consistently for some time. So I think we found
the maintainer :)

Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Breno Leitao <leitao@debian.org>
Signed-off-by: David S. Miller <davem@davemloft.net>