MAINTAINERS: Update my email address

My Intel email will stop working in a not too distant future. Move my
MAINTAINERS entries to my kernel.org address.

Signed-off-by: Björn Töpel <bjorn@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210115104337.7751-1-bjorn.topel@gmail.com